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BULLOUGH, W. S. 1960. Practical invertebrate anatomy. 2nd ed. London: Macmillan.

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FIscHER, P.-H., DUVAL, M. & Rarry, A. 1933. Etudes sur les échanges respiratoires des littorines. — Archs

Zool. exp. gén. 74: 627-634.

Konn, A. J. 1960a. Ecological notes on Conus (Mollusca: Gastropoda) in the Trincomalee region of Ceylon. —

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Konn, A. J. 19605. Spawning behaviour, egg masses and larval development in Conus from the Indian Ocean. —

Bull. Bingham oceanogr. Coll. 17 (4): 1-51.

THIELE, J. 1910. Mollusca: B. Polyplacophora, Gastropoda marina, Bivalvia. In: SCHULTZE, L. Zoologische

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Jena: Fischer.— Denkschr. med.-naturw. Ges. Jena 16: 269-270.

(continued inside back cover)

ANNALS OF THE SOUTH AFRICAN MUSEUM

ANNALE VAN DIE SUID-AFRIKAANSE MUSEUM

Volume 69 Band

April 1976 April

Part 8 Deel

THE CRANIAL AND CERVICAL MUSCLES OF THE

SOUTH AFRICAN LIMBLESS LIZARD

TYPHLOSAURUS AURANTIACUS AURANTIACUS

PETERS (REPTILIA, SAURIA)

JURI A. VAN DEN HEEVER

Cape Town Kaapstad

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Court Road, Wynberg, Cape Courtweg, Wynberg, Kaap

THE CRANIAL AND CERVICAL MUSCLES OF THE SOUTH AFRICAN

LIMBLESS LIZARD TYPHLOSAURUS AURANTIACUS AURANTIACUS

PETERS (REPTILIA, SAURIA)

JURI A. VAN DEN HEEVER

South African Museum, Cape Town

(With 18 figures)

LMS accepted 25 November 1975]

ABSTRACT

The skull and cervical vertebrae of Typhlosaurus aurantiacus aurantiacus exhibit marked

adaptations to a fossorial mode of life which is reflected in the associated musculature. Neither

eye muscles nor supratemporal arches are present. The adductor musculature of the jaws,

compacted into the temporal region, are dominated by two tripartite tendons, the bodenapo-

neurosis and the quadrate tendon. The m. pseudotemporalis is single. The m. cervicoman-

dibularis is probably the major jaw opening muscle. Posttemporal fenestrae are absent and

the cervical musculature encroaches far anteriorly on to the bulbous occiput. Discussed in

terms of a lever of the third class the action of the jaw shows great similarity to that of a

non-fossorial skink like Mabuia, and probably functions in an identical manner. Primary

adaptations for a fossorial mode of life appear to be the strengthening and streamlining of the

skull, loss of limbs and limb girdles and general attenuation of the body.

CONTENTS

Ibntirorlteivon 5 5 o o o 6 ». oe 9.'o LG

Material and methods Fel ete Lia as Wee a TA

Description

Osteology

@ranialvosteologyauw= ed Gu eel

@ervicalkosteolosy 9 5 92 4 ee 79

Myology

Muscle classification and nomenclature . 181

Constrictor dorsalis group. . . . . 182

Adductor mandibulae group . . . . 184

Intermandibular musculature. . . . 194

Pongsueimusculatures 5) 4) ee 19D

Depressor mandibulae group . . . . 4197

€ervicalimusculature, 4 2) 2) a 2 202

Discussion and conclusions . . . . . .. . 204

AcknowledsementSimai)s) neue ec ene 20)

ING ne Ne ee Be eGR he eee eee ee IG)

Abbreviatlonsm@eemes | sence) bt les) wea nee

INTRODUCTION

~The doubtful taxonomic position of Typhlosaurus has been dealt with by

various authors. Boulenger (1887) regarded the genus as related to Acontias but

placed it, like Gadow (1901), together with Anelytropsis and Feylinia in the

family Anelytropidae, close to the Scincidae. Camp (1923) places Typhlosaurus

169

Ann. S. Afr. Mus. 69 (8), 1976: 169-214, 18 figs

170 ANNALS OF THE SOUTH AFRICAN MUSEUM

in the Feyliniidae, within the superfamily Scincoidea, together with the Scin-

cidae, the Anelytropsidae and the Dibamidae.

Hewitt (1929), De Witte & Laurent (1943) and FitzSimons (1943) also

refer the genus to the Scincidae and according to Smit (in press) FitzSimons

regards Typhlosaurus as derivable, via Aconthophiops, from Acontias. Romer

(1956) rather doubtfully includes Typhlosaurus within the Scincidae. Greer

(1970), on the basis of the external morphology and cranial osteology especially

the relationship of the frontal bones and the bones of the secondary palate,

regards Acontias, Aconthophiops and Typhlosaurus as a subfamily of the Scinci-

dae, i.e. the Acontinae. Broadley (1968) agrees with FitzSimons and states:

‘The genus Typhlosaurus appears to have been derived from an ancestral form

of Acontias, after passing through an intermediate stage which is demonstrated

by the monotypic genus Aconthophiops. According to Smit (1964) the close

relationship between 7yphlosaurus and Acontias is abundantly confirmed by

the cranial osteology of 7. caecus, indicating that the genus Typhlosaurus

undoubtedly belongs within the Scincidae.

The following classification is thus adopted.

Class: Reptilia

Order: Squamata

Suborder: Sauria

Family: Scincidae

Subfamily: Acontinae Greer, 1968

Genus: Typhlosaurus Wiegmann, 1834

Species: T. aurantiacus Peters, 1882

Subspecies: 7. aurantiacus aurantiacus Broadley, 1968.

Limbless skinks of the genus Typh/osaurus are confined to southern Africa

(Broadley 1968). Eight species were recorded by FitzSimons (1943), and one

additional species, the greatly attenuated 7. braini from the Namib Desert,

was described by Haacke (1964). Subsequently Broadley (1968) revised the

genus, recognizing eight species placed into three species groups.

The genus as a whole is fossorial and according to Mertens (1955) only

appears on the surface towards evening. Their diet includes small insects and

myriapods of which small beetle latvae and termites form the most important

groups (Broadley 1968).

The cranial osteology of the fossorial Scincidae and forms with scincid

affinities, such as Dibamus, are well known from the work done on Acontias

(De Villiers 1939; Brock 1941; Van der Merwe 1944), Dibamus (Gasc 1968;

De Weerdt 1971), Typhlosaurus (Smit 1964), Feylinia (Du Toit 1971), Typhla-

contias (Cluver 1965), Melanoseps (Boyd 1969) and Scelotes (Leonard 1973).

The postcranial skeleton is less well known and except for the work of

Gase (1967a, b, c; 1968) and Hofstetter & Gasc (1969) has attracted few

Investigators,

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS neal

Myological studies on limbless lizards are few and far between. According

to Auffenberg (1962) there is no record of the axial muscles of limbless lizards

up to that time. Except for the work of Gasc (1968), De Weerdt (1971) and

Leonard (1973) the cranial muscles of limbless lizards are largely unknown.

De Weerdt’s account differs from the more detailed description of Gasc. How-

ever, Gasc’s description is difficult to evaluate in the light of comments given

by Haas (1973), and Leonard discusses only the eye muscles in Sce/otes.

Haas (1973) reviews the jaw muscles of the Rhynchocephalia and the

Squamata stating that: *. . . detailed studies of the cranial muscles are lacking

for two families (or groups often considered to be families) of lizards, namely

the Anelytropsidae and the Feyliniidae’. Greer (1970) assigned these two groups

to the Scincidae as the subfamilies Acontinae and Feylininae. Together they

represent the fossorial Scincidae of which the above statement is certainly true.

The previously mentioned studies have shown that a fossorial habit pro-

duces distinctive skeletal changes. Change in skeletal proportions should

inevitably affect associated musculature and in view of this fact the acute lack

of literature on the myology of fossorial Scincidae is believed to sufficiently

justify this paper.

MATERIAL AND METHODS

Three alcohol-fixed specimens of Typhlosaurus aurantiacus were obtained

from the South African Museum. One specimen was dissected and the skull

and postcranial skeleton were used for comparative and photographic purposes.

Both the other specimens were decalcified for a period of seven days in 7,5 per

cent solution of nitric acid in 70 per cent alcohol. Subsequently the specimens

were separately dehydrated, cleared in terpineol and embedded in paraffin wax

(52-54°C). Sectioned at 20 microns, one specimen gave excellent results; the

other proved of no use and was discarded. Staining and counter-staining were

done with the azocarmine-azan method and the enlarged drawings of the

sections were made with the aid of a camera lucida microscope attachment.

Owing to the paucity of material several specimens of the related but

more abundant genus Acontias were dissected to elucidate gross topography.

DESCRIPTION

OSTEOLOGY

Cranial osteology

The skull of Typhlosaurus caecus, which closely resembles that of

T. aurantiacus, was described by Smit (1964), and the reader is referred to this

paper for a comprehensive account of the cranial osteology. However, prior

to embarking on a description of the myology, the cranial and the cervical

osteology merit a few additional remarks on certain areas important to muscle

attachments, where Smit’s description is inadequate for the purpose of this

paper

172 ANNALS OF THE SOUTH AFRICAN MUSEUM

T. aurantiacus has the elongate skull and reduced orbits common to

attenuate fossorial lizards (Figs 1A—B, 2A). The eyes are visible as inconspicu-

ous black dots through the transparent integument and are devoid of associated

musculature. However, an optic nerve is present and the retinal pattern resembles

Fig. 1B. Stereophotographs of Typhlosaurus aurantiacus skull; lateral view.

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS Ws

that of amphisbaenids, in which light perception has been demonstrated by

Bonin (1965).

Fig. 2B. Stereophotographs of Typhlosaurus aurantiacus lower jaw;

lingual view.

174 ANNALS OF THE SOUTH AFRICAN MUSEUM

No remnants of lacrimal bones were found. The supratemporal arch is

absent but both the squamosal and supratemporal bones are present as small,

flattened, slightly overlapping elements dorsal to the quadrate.

The squamosal, lying anterolateral to the supratemporal, is tendinously

connected to the quadrate head (Figs 3, 13). The supratemporal lies postero-

medial to the squamosal and shares with the much reduced paroccipital process

of the otic capsule the articulation with the quadrate head by means of a pad

of fibrocartilage (Fig. 3).

PAR

Fig. 3. Posterolateral view of the skull.

The proportions of the posterior half of the skull are of importance. The

temporal region, where the adductor musculature is accommodated, is laterally

compressed and the otico-occipital region is much expanded both laterally

and posteriorly (Figs 1!A—B, 2A). These relations create the impression that the

suspensorium is more anteriorly located than in a non-fossorial lizard such as

Mabuia. The entire posterior border of the parietal meets the supraoccipital

and the fused exoccipital-opisthotic complex in a dorsally lying suture. There

is thus no posttemporal fenestra and the back of the skull is smooth and bluntly

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 175

rounded (Fig. 1A). Immediately below the foramen magnum a kidney-shaped

condyle is present, composed laterally of the exoccipitals and medially of a

suturally distinct basioccipital bone. Ventrally the basioccipital forms the

posterior portion of the skull base, curving upwards to meet the exoccipital

ventrolaterally to the condyle.

A tympanum and middle ear cavity are absent. The columella is massive,

consisting of a large footplate and a short anterolaterally directed stapes

(Figs 3-4), which extends laterally beyond the quadrate as a rod-like carti-

laginous extracolumella, terminating a short distance anterior to the quadrate

Fig. 4. Posteroventral view of the skull.

and ventrolateral to the medius portion of the external adductor muscle (Figs 5,

7-8, 12-13). The tendinous sheath surrounding the extracolumella is joined to

the retroarticular process of the lower jaw as in Typhlosaurus caecus (Smit 1964)

and Acontias meleagris (De Villiers 1939; Brock 1941; Van der Merwe 1944),

and is suspended anteriorly by a ribbon of fascia overlying the tendinous

covering of the adductor musculature and attaching to the dorsolateral border

of the parietal (Figs 5, 7-8, 12). The same condition exists in T. caecus and

T. lineatus.

176 ANNALS OF THE SOUTH AFRICAN MUSEUM

Fig. 5. Lateral superficial view of musculature.

The quadrate ramus of the pterygoid is gutter-shaped, with the trough

directed medially in the region of the basipterygoid joint to receive the basi-

pterygoid process. Posteriorly the quadrate ramus is twisted through ninety

degrees so that the trough faces ventrally where the posterolateral extremity

of the bone is tendinously connected to the ventromedial surface of the quadrate

(Fig. 4).

The anterior border of the quadrate is gently rounded for the attachment

of the lateral lamina of the quadrate tendon, while the posterior border of the

bone is concave to accommodate the laterally protruding stapes (Fig. 3).

Ventrally the large quadrate condyle articulates synovially with the lower jaw.

Dorsal to the attachment of the quadrate ramus of the pterygoid the medial

surface of the quadrate is slightly concave to accommodate the origin of the

posterior adductor muscle (Fig. 13). Dorsally the posterior part of the quadrate

head articulates synovially with both the supratemporal and the otic capsule

(Figs 3, 14).

The anterior part of the quadrate head is separated from the cranium by

fibres of the medius portion of the external adductor muscle and serves for

the origin of the vertical lamina of the quadrate tendon. The central part of

the quadrate head is tendinously attached to the squamosal (Figs 3, 13).

The thin, rod-like epipterygoid fits ventrally into the columellar fossa on

the dorsal surface of the pterygoid, lateral to the basipterygoid joint. Both

condylar surfaces are capped by cartilage. The dorsal extremity of the bone

attaches tendinously to the lateral surface of the parietal downgrowth immedi-

ately in front of the anterior superior process of the pro-otic (Fig. 4).

Because of the importance of the mandibular muscle insertions it is neces-

sary to augment the brief description of Smit (1964) of the lower jaw of Typhlo-

Saurus caecus. Each ramus consists of the normal six bones, viz. dentary,

coronoid, splenial, surangular, angular and a fused articular-prearticular, to

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS Loi

which the surangular is also partially fused (Fig. 17). Between the coronoid

process and the glenoid fossa both dentary and surangular bulge laterally,

forming a dorsolateral mandibular shelf on to which elements of the adductor

musculature insert (Fig. 11). Posteriorly, at the insertion of the pterygomandi-

bularis muscle, the ventral border of the jaw is concave (Fig. 17).

The dentary extends from the symphysis to the supra-angular foramen and

constitutes the anterior portion of the mandibular shelf (Figs 9-10). It carries

eight to nine pleurodont teeth, contributes the lateral half of the coronoid

process and is medially recessed along its posterior half to accommodate the

remaining lower jaw bones (Fig. 17). It is pierced laterally and antero-ventrally

below the tooth row by a line of four mental foramina, and postero-medially

by a large foramen transmitting the anterior mylohyoid nerve and the lingual

branch of the inferior alveolar nerve; anteromedially there are foramina for the

Meckelian cartilage and the anterior tip of the inferior alveolar nerve. The

position of the posteromedial foramen varied in the two Typhlosaurus auranti-

acus specimens investigated. In the serially sectioned skull the anterior process

of the coronoid bone and the anterior tip of the splenial form the posterior

border of the foramen, whereas, in the cleared specimen, the foramen lies well

within the boundaries of the dentary (Fig. 17). Behind the coronoid process,

fibres of the posterior adductor muscle and the medius portion of the external

adductor muscle insert along the dorsolateral border of the dentary.

The coronoid lies midway along the mandible, flattened medially against

the dentary, prearticular and surangular. Its coronoid process is a prominent

vertical sheet lying against the coronoid process of the dentary (Figs 2B, 9).

Ventrally the bone is braced against the action of the adductor muscles by an

anterior and a posterior process, the former bridging the dentary-prearticular

suture and the latter the surangular-prearticular suture (Fig. 17). Two parallel,

near-vertical grooves are present on the trailing edge of the coronoid process.

Separated by a ridge, they continue posteroventrally on to the medial side of

the posterior process; the more lateral of the two grooves receives the insertion

of the medius portion of the external adductor muscle while the pseudotem-

poralis muscle inserts into the medial groove (Figs 10, 17).

The surangular (Figs 9-12, 17) lies posteromedially to the dentary, postero-

laterally to the coronoid, dorsally to the prearticular and anteriorly to the

articular. Laterally it forms the posterior section of the mandibular shelf

(Fig. 11) and dorsally it bears a ridge extending between the coronoid and the

articular processes. Its anterior extremity underlies the coronoid process while

in addition to covering the Meckelian canal up to the adductor fossa, the

posterodorsal tip of the bone constitutes the anterior part of the articular

process. Posteromedially the bone forms the dorsal border of the adductor

fossa and is laterally pierced by the posterior supra-angular foramen, which

leads from the adductor fossa, and the anterior supra-angular foramen which

leads from the Meckelian canal. The posterior adductor muscle and medius

portion of the external adductor muscle insert on the dorsomedial and dorso-

178 ANNALS OF THE SOUTH AFRICAN MUSEUM

LCE RP Oc

Fig. 6. Dorsal superficial view of the cervical musculature; spinalis capitis muscle removed

on the right side.

lateral surfaces of the surangular. Posteriorly the bone is fused to the articular-

prearticular complex.

The splenial (Figs 9-10) is a thin sliver of bone on the inner surface of

the jaw in line with the coronoid process. It lies posteromedially to the dentary,

medially to the prearticular, dorsally to the angular and ventrally to the coro-

noid. It is devoid of any muscle insertions and neither bears foramina nor

contributes to the inner wall of the Meckelian canal.

The angular (Figs 9-10, 11, 17), a narrow ventral element below the pre-

articular and splenial, lies with its anterior tip within the dental recess and

traverses the jaw posteroventrally between the prearticular and dentary to

terminate posteriorly on the lateral surface of the mandible, ventral to the

posterior tip of the surangular. Between the prearticular and dentary it forms a

narrow medial section of the floor of the Meckelian canal, from the adductor

fossa to immediately anterior to the coronoid process. At its midpoint it is

pierced ventrally by the posterior mylohyoid foramen, which transmits the

posterior mylohyoid nerve.

The prearticular (Figs 11-12, 17) lies ventrally to the surangular, postero-

medially to the dentary, dorsally to the angular and laterally to the coronoid

and the splenial. It forms most of the medial wall and part of the floor of the

Meckelian canal as well as the ventral border of the adductor fossa. Medially

it receives the insertion of the adductor musculature and posteriorly it is com-

pletely fused to the articular.

Behind the glenoid fossa the articular-prearticular (Figs 13-17) forms the

spoon-shaped retroarticular process, which receives the insertion of the ptery-

goideus muscle on its medial and lateral surfaces and that of the depressor

mandibulae muscle on the dorsal surface. The glenoid fossa, lined with cartilage,

lies in front of the insertion of the depressor mandibulae muscle and behind and

against the articular process. The foramen for the chorda tympani lies medially

on the retroarticular process, with its canal extending anteriorly through the

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 179

bone to open into the adductor fossa.

The hyoid apparatus in Typhlosaurus aurantiacus is a triradiate, carti-

laginous structure resembling a tuning-fork with posteriorly divergent prongs.

It lies ventral to the trachea and extends posteriorly from the glottis to a point

in line with the posterior border of the pterygoideus muscle. Anteriorly, in the

ventral midline, the lingual process (proc. entoglossus) supports the tongue

musculature (Figs 9-10).

No part of the hyoid apparatus is ossified and the structure could conse-

quently not be divided with certainty into the various components commonly

found in reptiles. From the work of Van der Merwe (1944), Langebartel (1968)

and De Weerdt (1971) it appears that the paired posterior prongs represent

the first ceratobranchials.

Cervical osteology

Vertebrae and ribs are highly variable structures and in the limbless

squamates the regional differentiation of the vertebral column has lead to

various interpretations of the cervical vertebrate. Zangerl (1945) recognizes

four vertebral divisions in the Amphisbaenidae, i.e. cervical, thoraco-lumbar,

cloacal and caudal. The cervical region includes all the anterior ribless verte-

brae, i.e. atlas, axis and one to two of the following vertebrae, whilst the thoraco-

lumbar region includes all vertebrae with movable unforked ribs. Sood (1948)

divides the ophidian vertebral column into a precaudal and a caudal region

of which the former is subdivided into cervical, thoracic and lumbar sub-

regions. The cervical sub-region consists only of the atlas and the axis whereas

the thoracic region includes all vertebrae following the axis and which bear

hypapophyses. List’s (1966) description of the burrowing snakes follows

Zangerl (1945) in defining the regions of the vertebral column. Consequently

he defines the cervical region in burrowing snakes as consisting only of the

atlas and the axis since the vertebrae following the axis bear unforked ribs

and are therefore included in the thoraco-lumbar region. List notes that although

this system appears satisfactory for the Typhlopidae and Leptotyphlopidae its

use is limited in that it cannot be directly applied to other vertebrates.

According to Gasc (1968) and Hofstetter & Gasc (1969) the cervical

vertebrae can only be defined as those vertebrae preceding the vertebrae carrying

the first rib attached to the sternum. These authors refer to the work of Stannius

(1849) and state that all other definitions of cervical vertebrae such as ribless

anterior vertebrae, vertebrae with hypapophyses or ribless vertebrae plus

vertebrae with short ribs are invalid because too many exceptions and contra-

dictions are involved.

Limb regression is usually accompanied by regression of the girdles and

in certain of the fossorial Scincidae, e.g. in the genus Typhlosaurus, this phe-

nomenon is rather pronounced. In Feylinia the ribs of the eighth vertebra are

still attached to a vestigial sternum (Gasc 1965), in Dibamus the pectoral girdle

is connected to the fifth vertebra (Gasc 1968) and in Acontias meleagris the

180 ANNALS OF THE SOUTH AFRICAN MUSEUM

; \EM \eIS

— =|

Imm

Fig. 7. Ventrolateral view of the superficial neck musculature.

vestigial girdle is united by the serratus muscle to the second and the third ribs.

In T. vermis the pectoral girdle is absent (Hofstetter & Gasc 1969). In T. auran-

tiacus the pectoral girdle is aiso absent, and the ribs consequently lack sternal

attachments. It is therefore not possible to define a specific cervical region

within the vertebral column of 7. aurantiacus. In limbless squamates such as

ophidians (completely lacking a pectoral girdle) and amphisbaenids (lacking

sternal attachments of the ribs) Hofstetter & Gasc (1969) divide the vertebral

column into precloacal, cloacal and caudal regions.

In this paper the term ‘cervical’ does not define a region of the vertebral

column but refers only to that area on the precloacal region of the vertebral

column from which the musculature responsible for the movements of the head

arise.

Typhlosaurus aurantiacus has procoelous vertebrae as in all saurians

except the Gekkonidae. The broad elliptical condyles are slightly dorsally

orientated and are as wide as the centra of the vertebrae. The first pairs of ribs

are carried by the third vertebra, as in Acontias meleagris.

The ribs are holocephalous (unicipital) and each has two tuberculiform

processes close to the costal head; one anteroventrally and one postero-

dorsally for the attachment of the intercostal muscles. A similar condition

exists in T. vermis (Hofstetter & Gasc 1969). As a result of the increased func-

tional importance of the cervical musculature in a limbless burrower such as

T. aurantiacus, the synapophysis of the axis and the following three vertebrae

are laterally extended to enlarge the area of origin of the cervical musculature.

The atlas consists of paired neural arches and a ventral intercentrum.

A neural spine is absent and the two semilunate neural arches do not fuse

dorsally. No functional zygapophyses are present between the atlas and the

axis, although the atlas has a small process on the posterolateral margin of

the neural arch in a similar position to the postzygapophyses of the other

vertebrae.

The axial centrum bears two hypapophyses, of which the posterior one

is probably derived from the intercentrum of the third vertebra as Holder

(1960) found in gekkos. Anterolaterally the neural arch has a small process

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 18]

coinciding with the position of the prezygapophyses on the vertebrae following

the axis. The neural spine resembles the blade of an axe and extends the full

length of the neural arch.

Midventrally on the centra of each of the seven vertebrae following the

axis a hypapophysis is present. The neural spines, posterodorsally situated

on the neural arches, extend obliquely caudally. The vertebrae articulate by

DMA

ae ae a

—S

Fig. 8. Lateral view of the deep cervical musculature.

means of pre- and post-zygapophyseal processes and no zygosphene-zygantrum

type of articulation, as found in snakes and some saurian families, is present

in Typhlosaurus aurantiacus.

MYOLOGY

Muscle classification and nomenclature

The currently accepted classification of visceral cranial muscles is based

on Vetter’s (1874, 1878) and Ruge’s (1897) studies on selachians. The Constrictor

superficialis (Cs) is subdivided into segmentally innervated portions, i.e. the

trigeminus muscle complex as the Constrictor superficialis I (Cs,); the facial

muscles as the Constrictor superficialis II (Cs); the glossopharyngeal muscles

as the Constrictor superficialis III (Cs,); and the vagus muscles as the Constrictor

superficialis IV-VIHI (Cs,_,). Luther (1914) extended this classification to

tetrapods and introduced a subdivision of the jaw adductors based on the

spatial relationships of the muscles with the three rami of the trigeminal nerve.

This system has been generally accepted for sauropsids by most authors includ-

ing Adams (1919), Lakjer (1926), Haas (1930, 1934, 1973), Lubosch (1933),

Edgeworth (1935), Brock (1941), Save-Séderbergh (1945), Ingeborg Poglayen-

Neuwall (1953, 1954), Ivo Poglayen-Neuwall (1953a, 19535), Oelrich (1956),

Ostrom (1961), Gasc (1968) and Barghusen (1973). In sauropsids the Con-

strictor I is divided into the m. constrictor I dorsalis (M.C,d), the m. constrictor f

182 ANNALS OF THE SOUTH AFRICAN MUSEUM

lateralis (M.C,l) represented by the m. adductor mandibulae, and a m. con-

strictor I ventralis (M.C,v), the m. intermandibularis.

The constrictor I dorsalis (M.C,d) extends between the cranium and the

movable palatal complex. This group of muscles is involved with kinetic move-

ments of the skull and they are variable in their occurrence.

Basically, the constrictor I lateralis (M.C,l), the m. adductor mandibulae

of sauropsids, is divided into an external, and internal and a posterior muscle.

The external adductor is usually suodivided into three portions, i.e. super-

ficialis, medius and profundus. The internal adductor commonly consists of

two, well-separated muscles, the m. pseudotemporalis and the m. pterygoideus.

The posterior adductor is usually a single muscle.

The constrictor I ventralis (M.C,v), the m. intermandibularis, is situated

between the rami of the lower jaws, superficial to the throat musculature, and

is subdivided into an anterior and a posterior portion.

Lubosch (1933) recongizes three basic arrangements of jaw muscles, i.e.

selachian, amphibian and mammalian, of which the jaw muscles of sauropsids

belong to the amphibian type. Homologies between the three types are uncertain,

according to Haas (1973), and are further complicated by the varied nomen-

clature in existence for saurian jaw musculature. For a complete list of syno-

nyms see Lakjer (1926), Edgeworth (1935) and Haas (1973).

Nishi (1919) laid down the terminology for axial musculature and, together

with Vallois (1922), is amongst the few workers who have approached axial

musculature on a comparative basis. More recent accounts are those of Olson

(1936) and Evans (1939).

Reptilian epaxial musculature is divisible into three longitudinal systems.

Dorsomedially the transversospinalis system lies lateral to the spinous pro-

cesses of the vertebrae, the longissimus system lies lateral to the transverso-

spinalis system and dorsal to the heads of the ribs, and the iliocostalis system

lies on the ribs dorsal to the upper margin of the external oblique abdominal

muscles. Anteriorly, towards the occiput, the epaxial musculature breaks down

into various shorter groups of fibres, the cervical muscles, which insert pos-

teriorly on to the skull and are responsible for the movements of the head.

The hypaxial musculature does not fall within the scope of this paper.

Constrictor dorsalis group (C,d)

This group of muscles lies deep to the adductor musculature and is respon-

sible for the intercranial kinetic movements of the skull. The muscles arise,

in Versluys’ (1912) terminology, on the occipital segment of the skull and insert

on to the maxillary segment. In Typhlosaurus aurantiacus the group is repre-

sented by a minute m. levator pterygoidei and a large m. protractor ptery-

goidei. A levator bulbi muscle is absent.

The small m. levator pterygoidei (Ip, Figs 9-10), roughly triangular in

transverse section, lies laterally to the basipterygoid joint, the opthalmic ramus

of the trigeminal nerve, the palatine ramus of the facial nerve, the internal

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 183

PAR

aXe)

Zo 02

AX. oS°

GH, = © y

GHM

Fig. 9. Cross-section of the skull at the level of the coronoid process.

carotid artery and the origin of the protractor pterygoidei muscle; medially

to the pseudotemporalis muscle, the anterior part of the pterygoideus muscle

and the epipterygoid. It lies against the medial surface of the epipterygoid

with the posterior border of the muscle in line with that of the bone.

184 ANNALS OF THE SOUTH AFRICAN MUSEUM

The muscle arises as a ribbon of fascia from the lateral surface of the pro-

otic membrane, ventral to the lateral parietal downgrowth, medioventral to

the dorsal extremity of the epipterygoid bone and anteroventral to the anterior

superior process of the pro-otic.

The insertion is fleshy and bridges the palatine-pterygoid suture dorsally.

Anteriorly it attaches on to the posterolateral border of the palatine bone,

medially to the anterior extremity of the pterygoideus muscle, and posteriorly

it attaches on to the anterodorsal surface of the pterygoid bone medially to

the columellar fossa.

A nerve seen within the muscle in transverse section was too small for its

connections to be traced.

The large m. protractor pterygoidei (prp, Figs 11-14) lies behind the

the basipterygoid process, the individual fibres extending obliquely between

the lateral margin of the skull base and the full length of the quadrate ramus

of the pterygoid. The muscle is situated posteromedially to the levator ptery-

goidei muscle, medially to the mandibular ramus of V, dorsally to the ptery-

goideus muscle, ventrally to the Gasserian ganglion and the proximal part of

the opthalmic ramus, and laterally to the parasphenoid-basisphenoid complex,

the otic capsule, the palatine ramus of VII, and the internal carotid artery.

The muscle arises fleshily from the dorsal surface of the basipterygoid

process, the lateral surfaces of the parasphenoid-basisphenoid complex and

the anterior inferior process of the pro-otic, and anteroventrally from the

lateral surface of the pro-otic proper (Figs 9-11). Anteroventrally within the

muscle a flat tendon is present which arises ventrally on the basipterygoid

process. Fibres arise from both dorsal and ventral surfaces of the tendon.

The insertion is confined to the quadrate ramus of the pterygoid bone

posterior to the basipterygoid process. Fibres insert along the inner concave

surface and the dorsal surface of the ramus. An insertional tendon is present

within the muscle, posterodorsally to the tendon of origin, the fibres insert

on to its dorsal and ventral surfaces. This tendon attaches to the dorsal (inner)

rim of the quadrate ramus (Figs 11—12).

The muscle is innervated by a separate branch of V leaving the Gasserian

ganglion ventrally, piercing the muscle dorsally and coursing anteriorly a short

distance before ramifying.

Adductor mandibulae group

Compared with non-fossorial lizards, the adductor musculature as exemplified

by Typhlosaurus aurantiacus is modified to function as a compact unit within

the temporal indentation. The external adductors are dominated by two oblique,

parallel tendons, of which the anterodorsal one is a modified bodenaponeurosis.

It arises as a single tendon on the coronoid process of the lower jaw (Fig. 9),

posterior to which it fans out into the external adductor mass as three laminae.

In transverse section this unit appears as a tripartite structure resembling an

inverted Y (Fig. 11). The three laminae serve as areas of insertion to the external

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 185

and internal adductors and will be referred to in the text as the vertical, medial

and lateral laminae of the bodenaponeurosis.

The second tendon (Figs 11-12), located posteroventrally to the bodenapo-

neurosis, also shows a tripartite configuration. It arises on the quadrate and

extends anteroventrally to just posterior to the base of the coronoid process.

This tendon will be referred to as the quadrate tendon and its laminae as the

vertical, medial and lateral laminae of the quadrate tendon. Each lamina has a

separate origin from the quadrate. The vertical lamina arises from the dorsal

midline of the quadrate, piercing the medius portion of the external adductor

muscle ventromedially. The lateral lamina arises from the anterior border of

the bone and the medial lamina along its inner dorsal surface (Fig. 13), covering

the medial surface of the posterior adductor fibres arising from the medial

surface of the quadrate.

Ventrolaterally to the superficial portion of the external adductor and

anteromedially to the extracolumella, a ligament is present in the position

of the quadrato-maxillary ligament as described by Ingeborg Poglayen-Neuwall

(1953) and Haas (1960). In Typhlosaurus aurantiacus, however, this ligament

arises ventrolaterally from the lateral lamina of the bodenaponeurosis and

extends anteriorly within the upper lip (Figs 5, 7-8), terminating laterally to

the premaxillary. Ventrolaterally to the orbit the integument turns under this

ligament to form the angle of the mouth.

A small horizontal bundle of muscle fibres is associated with the extra-

columella (Fig. 12). It lies in a somewhat similar position to the m. retractor

anguli oris of the amphisbaenids Amphisbaena and Leposternon as described

by Lakjer (1926). However, in Typhlosaurus aurantiacus these fibres extend

between the anteromedial surface of the extracolumella and the lateral lamina

of the bodenaponeurosis and they apparently function to draw the extra-

columella against the lateral surface of the adductor musculature.

The three major divisions of the adductor mandibulae group are readily

identified by virtue or their spatial relationship with the three rami of the

trigeminal nerve (Luther 1914). In Typhlosaurus aurantiacus the external adduc-

tor muscle mass lies laterally to the maxillary and mandibular rami (Figs 10-12),

the internal adductor lies medially to the maxillary but laterally to the ophthal-

mic rami (Fig. 9), and the adductor posterior lies laterally to the mandibular

ramus and ventrally to the external adductor (Fig. 12).

Musculus adductor mandibulae externus

The external adductor musculature arises within the temporal indentation

and its origin is bordered dorsally by a curved ridge on the parietal, extending

from the posterior tip of the postfrontal to the posterior extremity of the parietal

(Figs 9-14).

Three portions of the external adductor musculature—the superficialis,

medius and profundus—are present, either separated by tendinous laminae

or by differences in fibre orientation,

186 ANNALS OF THE SOUTH AFRICAN MUSEUM

The musculus adductor mandibulae externus superficialis (aes, Figs 9-11),

the most lateral portion of the external adductor, lies partially anterior to the

medius and profundus portions. Posteriorly, it is separated from them by, respec-

PAR

RMA

PAL

Fig. 10. Cross-section of the skull just behind Figure 9.

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 187

tively, the lateral and the vertical laminae of the bodenaponeurosis. Anteriorly

the superficialis lies lateral to the pseudotemporalis muscle and is separated

from it by the maxillary ramus of the trigeminal nerve. Dorsal to the vertical

lamina of the bodenaponeurosis there is no distinction, other than fibre orien-

tation, between the superficialis and profundus portions. The superficialis,

however, is readily identified by the dorsoventral arrangement of its fibres as

opposed to the anteroventral orientation of the profundus fibres. The two

portions are by no means confluent since they separate easily during dissection.

The most substantial part of the superficialis lies dorsal to the coronoid process,

resulting in a near vertical fibre orientation relative to the long axis of the

lower jaw (Fig. 9).

The superficialis portion arises from the ventral surface of the postfrontal

(Fig. 9), from the dorsolateral ridge on the parietal (Fig. 11) and from the

lateral surface of the profundus portion. The origins are fleshy throughout.

Insertion is effected laterally on to the vertical and lateral laminae of the

bodenaponeurosis (Fig. 9), from the coronoid process posteriorly to a point

dorsal to and almost in line with the anterior tip of the extracolumella.

The superficialis portion is innervated by a posterolateral branch of the

mandibular ramus of V, which runs anterodorsally through the medius portion

to enter the medial surface of the superficialis portion via the medial lamina of

the bodenaponeurosis.

The musculus adductor mandibulae externus medius (aem, Figs 11-14)

lies posterolaterally to the pseudotemporalis muscle and between the boden-

aponeurosis and the quadrate tendon, with the vertical lamina of the latter

piercing it along the ventromedial border. It extends anteroventrally from the

posterolateral border of the parietal to the lower jaw and, being the most ventral

portion of the external adductor muscle, its dorsal border is wedged between the

lower extremities of the superficialis and profundus portions, separated from

them by, respectively, the lateral and medial laminae of the bodenaponeurosis.

Ventrally the muscle is forked, straddling the lower jaw from the coronoid

process to the anterior border of the posterior adductor muscle. At this point

there is, for a short distance, no partition between the fibres of the medius

portion of the external adductor and those of the posterior adductor (Fig. 11).

However, the medius portion is distinctly separated from the posterior adductor

by the lateral and medial laminae of the quadrate tendon over practically its

entire length. Posterior to the bodenaponeurosis and dorsal to the quadrate,

the medius fibres are continuous with those of the more medially situated

profundus portion of the external adductor (Fig. 12). It can, however, be

determined with reasonable accuracy that most of the fibres in this area belong

to the medius portion.

The medius portion arises fleshily from the posterolateral surface of the

parietal (Fig. 12), the lateral surfaces of the supratemporal, the squamosal,

the pro-otic dorsal to the quadrate and the lateral surface of the quadrate

above the extracolumella (Fig. 13).

188 ANNALS OF THE SOUTH AFRICAN MUSEUM

The insertion remains fleshy throughout and the fibres attach on to the

inferior surfaces of the medial and lateral laminae of the bodenaponeurosis, the

superior surfaces of the medial and lateral laminae of the quadrate tendon, the

medial and lateral surfaces of the vertical lamina of the quadrate tendon, and into

Fig. 11. Cross-section of the skull at the level of the Gasserian ganglion.

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 189

the lateral groove on the coronoid (Fig. 10), with a few fibres attaching postero-

laterally on to the coronoid process of the dentary. Between the base of the

coronoid process and the foramen for the anterior supra-angular nerve, the

insertion utilizes the medial surface of the surangular, the dorsomedial surface

of the posterior process of the coronoid and a small dorsomedial area on the

prearticular, anterior to the adductor fossa. Dorsally the insertion continues

along the surangular ridge, anterior to the adductor fossa, as well as along

the dorso-lateral surface of the surangular and the dentary forming the

mandibular shelf. The diffuse nature of a small posterior part of the insertion

has been mentioned.

The medius portion is innervated by a posterolateral branch of the man-

dibular ramus of V piercing the muscle medially.

The musculus adductor mandibulae externus profundus (aep, Figs 11-12),

deepest portion of the external adductor, lies against the lateral cranial wall

laterally to the Gasserian ganglion and the maxillary ramus of the trigeminal

nerve, posterolaterally to the pseudotemporalis muscle, and medially to the

superficial and medius portions of the external adductor.

Extending anteroventrally, the profundus portion arises fleshily behind

the postfrontal, on the lateral surfaces of the parietal downgrowth and the

anterior superior process of the pro-otic (Fig. 11), as well as anterolaterally

on the pro-otic proper (Fig. 12). The area of origin is bounded dorsally by

the dorsolateral ridge of the parietal.

This muscle has no direct contact with the lower jaw and inserts fleshily

along the entire medial surface of the vertical lamina, and along the dorsal

half of the upper surface of the medial lamina of the bodenaponeurosis (Fig. 11).

Dorsally to the vertical lamina of the bodenaponeurosis no partition exists

between the superficial and profundus muscles (although the latter remains

discrete owing to the oblique orientation of its fibres, as opposed to the near

vertical orientation of the superficial fibres) (Fig. 11), whereas posterior to the

bodenaponeurosis no distinction is apparent between the profundus and medius

muscles (Fig. 12). However, the extent of each portion may be fairly easily

determined.

The profundus portion is innervated by a branch leaving the mandibular

ramus of V immediately below the Gasserian ganglion and turning dorsally

for a short distance to enter the muscle medially.

Musculus adductor mandibulae posterior

The posterior division of the adductor mandibulae group is present as a

single muscle, the musculus adductor mandibulae posterior (ap, Figs 11-13).

It extends anteroventrally from the quadrate to the mandible and lies laterally

to the mandibular ramus of the trigeminal nerve and medially to the extra-

columella (Fig. 12). It is straddled over its entire length by the medius portion

of the external adductor, although separated from it by the lateral and medial

laminae of the quadrate tendon (Fig. 11).

190 ANNALS OF THE SOUTH AFRICAN MUSEUM

Fig. 12. Cross-section of the skull at the level of the mandibular ramus of V.

The muscle arises fleshily from the slightly concave medial surface of the

quadrate, dorsomedially to and in line with the jaw articulation, as well as

dorsally to the posterior extremity of the protractor pterygoideus muscle and

the attachment of the quadrate ramus of the pterygoid (Fig. 13). The origin is

also ventrolateral to the pro-otic and anterior to the stapes, with a few of the

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 191

most dorsal fibres arising dorsally to the stapes (Fig. 14). Fibres also arise from

the anterior border of the quadrate. The quadrate tendon covers the posterior

adductor completely (Fig. 12) except at the anterior extremity of the muscle in

the region of the anterior supra-angular foramen where, over a short distance,

the fibres of the posterior adductor are continuous with those of the medius

portion of the external adductor. However, apart from obscuring the exact

anterior border of the insertion, this is of little importance since the muscles

are effectively separated, in practice, by the quadrate tendon. In addition, some

of the posterior adductor fibres arise from the inferior surfaces of the lateral

and medial laminae of the quadrate tendon.

The muscle inserts fleshily on to the mandible in an area extending from

the articular facet to the base of the coronoid process. Its posterior extremity

is pierced ventromedially by a small, robust tendon (Fig. 13), receiving the

MIO

Fig. 13. Cross-section of the skull at the level of the quadrate.

(G2 ANNALS OF THE SOUTH AFRICAN MUSEUM

insertion of the fibres arising in line with the jaw articulation on the medial

surface of the quadrate. This tendon extends anteriorly for a short distance to

attach immediately anterior to the articular facet on the dorsomedial surface

of the articular process. The rest of the fibres straddle the mandible and insert

dorsomedially on the surangular, within and around the adductor fossa (Fig. 11)

on that part of the prearticular forming the ventral rim of the adductor fossa,

and anterior to the fossa on the dorsomedial surface of the prearticular. A few

fibres attach dorsomedially to the posterior process of the coronoid. In addition,

fibres of this part of the muscle also insert on a small, vertical tendon running

dorsally along the surangular ridge and situated within the muscle itself (Fig. 11).

The tendon extends from the anterior border of the muscle to a point in line

with the anterior border of the mandibular ramus of V, and fibres insert along

its lateral and medial surfaces. The lateral fibres of the muscle insert on the

mandibular shelf (Fig. 11), attaching dorsolaterally on to the surangular and

dentary from the articular facet to near the base of the coronoid process.

A posterolateral branch of the mandibular ramus of V ramifies within

the medius portion of the external adductor, with one branch piercing the

medial lamina of the quadrate tendon to innervate the posterior adductor.

Musculus adductor mandibulae internus

According to Lakjer (1926) the third main division of the adductor man-

dibulae group, the internal adductor musculature, consists of two separate

muscles, the m. pseudotemporalis and m. pterygoideus. Both muscles are

present in 7yphlosaurus aurantiacus as well-defined groups of fibres situated at

right angles to one another.

The musculus adductor mandibulae internus pseudotemporalis (p, Figs

9-11) is a single, dorsoventral group of fibres located anteriorly within the

temporal indentation, and although the bulk of its fibres are concentrated

dorsomedially to the coronoid process, the muscle extends posteriorly to the

anterior border of the mandibular ramus of V. As required by the classical

definition it is situated medially to the maxillary, laterally to the ophthalmic

and anteriorly to the mandibular rami of V. It lies medially to and against

the superficial, anteromedially to the medius and anteriorly to the profundus

portions of the external adductors; anteromedially to the posterior adductor

muscle: laterally to the levator pterygoideus muscle and the epipterygoid bone,

and anterolaterally to the pterygoideus muscle.

It arises fleshily from the anterolateral surfaces of the parietal downgrowth

and the anterior superior process of the pro-otic, anterior to the origin of the pro-

fundus portion of the external adductor as well as from the lateral surface of

the pro-otic membrane and the dorsal part of the epipterygoid bone.

The muscle inserts on the medial surface of the coronoid bone, utilizing

the medial coronoid groove which extends from the apex of the coronoid

process to the medial surface of the posterior process of the coronoid bone

(Fig. 10). A small tendon attaching to the coronoid bone extends along the

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 193

lower rim of the medial coronoid groove and underlies the pseudotemporalis

muscle, receiving the insertion of its medial fibres (Fig. 9). Behind the coronoid

bone a few fibres insert on to the medial surface of the prearticular bone

(Fig. 11).

The muscle is innervated by a branch of the mandibular ramus of V which

leaves the anterior border of the ramus directly below the Gasserian ganglion

and courses anteriorly for a short distance to enter the muscle posterodorsally.

The musculus adductor mandibulae internus pterygoideus (pts), is the

largest single muscle in the head of Typhlosaurus aurantiacus and extends from

the infra-orbital fenestra to the posterior extremity of the mandible. It has a

small head which expands posteriorly to form a large rounded masticatory

cushion, appropriately termed ‘Kauwulst’ by Lakjer (1926). The ‘Kauwulst’

is the most prominent part of the muscle and, with its opposite number, limits

the aperture of the throat. It lies deep to the intermandibularis posterior muscle

and the mandibulo-hyoid musculature, medially to the insertional tendon of

the cervicomandibularis muscle and laterally to the protractor pterygoidei

muscle and the pterygoid bone.

The muscle arises mainly from the outer surface of the pterygoid bone

(Fig. 9) and from the inner surface of an extensive tendon originating lateral

to the infra-orbital fenestra. Anteriorly the muscle is divided into two short

slips, one arising dorsally from both the posterolateral surface of the palatine

and the anterolateral border of the pterygoid and the second one arising ven-

trally on the posterolateral border of the palatine and the anterolateral surface

of the pterygoid. The two muscle slips become confluent at a point in line with

the anterior border of the levator pterygoideus muscle.

Some fibres arise fleshily along the outer lateral and ventral surface of

the gutter-shaped pterygoid bone (Fig. 11). The major part of the origin,

however, is from the exceptionally strong tendon arising lateral to the infra-

orbital fenestra on the ventral surface of the palatal complex. The tendon arises

behind the ventrolateral process of the maxillary on the ventral surface of the

ectopterygoid, the posteroventral surface of the palatine and on the ventral

surface of the pterygoid in front of the basipterygoid recess. Anteriorly the

tendon covers the origin of the ventral slip of muscle and forms a thick pad

medial to the angle of the mouth (Fig. 9). The pad presumably protects the

fibres from damage by deflecting the coronoid process laterally during adduction

of the jaw. Posteriorly the tendon broadens to cover the anterior two-thirds

of the ventral surface of the muscle. Most of the fibres of the pterygoideus

muscle arise from the inner surface of this tendon.

The muscle inserts on the retroarticular process of the mandible (Fig. 13).

In front of the process the ventral border of the mandible is concave to accom-

modate the lateral fibres of the muscle which wrap around the jaw behind the

posteroventral extremity of the dentary. The muscle envelops the retroarticular

process, with fibres inserting on to its medial, ventral and lateral surfaces.

Medial to the jaw a ribbon-like tendon lies within the muscle and attaches

194 ANNALS OF THE SOUTH AFRICAN MUSEUM

ventrally to the retro-articular process (Fig. 13). Its dorsal and ventral surfaces

are utilized for insertion.

The muscle is innervated by a branch of V which leaves the mandibular

ramus medially, in line with the posterior supra-angular foramen, to pierce

the muscle laterally.

Intermandibular musculature

The intermandibular muscles, innervated by V, form part of the trigeminal

musculature. Situated anteroventrally to the constrictor colli, their fibres

extend transversely between the rami of the lower jaws as thin superficial sheets

of muscle, deep only to the skin and to the insertional tendon of the cervico-

mandibularis muscle. Two portions, an anterior and a posterior, are present.

The m. intermandibularis anterior (ia, Figs 9-10), four to six fibres in

thickness, lies anteriorly between the rami of the lower jaws. It is laterally

interrupted at right angles by bundles of the geniohyoideus muscle which insert

anteroventrally on the jaw. According to Camp (1923) these interdigitations

(of which there are five in Typhlosaurus aurantiacus) are always present in

lizards. The muscle lies superficially to the geniohyoideus and genioglossus

muscles and can be divided into a more posteriorly lying superficial portion

and a more anteriorly lying profundus portion.

The superficial portion arises medially on the jaw (Fig. 10) between the

posterior mylohyoid foramen and the combined foramen for the anterior

mylohyoid and the infra-alveolar nerves, along the medial surface of the pre-

articular, splenial and dentary bones. It inserts anteriorly along the ventral

midline onto the sheet of fascia receiving the insertion of the constrictor colli

muscle. Three bundles of geniohyoideus fibres interdigitate with the superficial

portion of the intermandibularis anterior muscle.

The profundus portion of the m. intermandibularis anterior lies imme-

diately anterior to the superficial portion, posteriorly overlain by the latter.

It arises medially to the jaw from the dorsolateral surface of the sublingual

gland and the outer surface of the buccal lining, dorsal to the gland. The origin

extends from a point in line with the anterior mylohyoid and the infra-alveolar

foramen to just behind the jaw symphysis. The muscle inserts tendinously

in the ventral midline anterior to the superficial portion of the intermandibularis

anterior muscle. Two bundles of the geniohyoideus fibres interdigitate with the

profundus portion.

The intermandibularis anterior is innervated by a branch of the posterior

mylohyoid nerve, which enters the superficial portion posteriorly, and by a

branch of the anterior mylohyoid nerve, which enters the profundus portion

superficially.

The m. intermandibularis posterior (ip, Fig. 12), two fibres in thickness,

lies immediately behind the intermandibularis anterior. The two muscles are

separated by the most posterior interdigitation between the geniohyoideus

and intermandibularis anterior muscles. The intermandibularis posterior does

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 195

not interdigitate with the geniohyoideus muscle and is well separated from the

constrictor colli. It covers the throat ventrally, lateral to the midline, and lies

superficially to the hyoglossus, the genioglossus and the geniohyoideus muscles,

the masticatory cushion (Kauwulst) of the pterygoideus muscle and the hypo-

glossal nerve (Fig. 12).

The m. intermandibularis posterior arises tendinously from a thin sheet

of fascia which covers the pterygoideus muscle laterally (Fig. 12) and attaches

to the lateral surfaces of the surangular and dentary bones between the jaw

articulation and the posterior mylohyoid foramen. The muscle inserts ten-

dinously in the ventral midline on to the same sheet of fascia which receives

the insertion of the constrictor colli muscle and the intermandibularis anterior

muscle (Fig. 12).

It is innervated by a branch of the posterior mylohyoid nerve, entering the

muscle superficially via the posterior mylohyoid foramen.

Tongue musculature

In Typhlosaurus aurantiacus the tongue is of the usual scincid type, bluntly

triangular with a bifurcate apex and posteriorly divided into two roots situated

lateral to the glottis. Behind the apex its dorsal surface is covered with scale-

like papillae, on which glandular surfaces are restricted to the basal portions.

According to Camp (1923) the position of the glandular surfaces is a diagnostic

feature of the Scincomorpha.

The tongue is composed of fibres of both extrinsic and intrinsic muscula-

ture. The intrinsic fibres control the shape of the tongue, while motion is

controlled by the extrinsic fibres. Sondhi (1958) found that in some Indian

reptiles the apparently distinct groups of intrinsic fibres are actually parts of

the hyoglossus muscle and do not deserve independent status. In Typhlosaurus

aurantiacus these fibre groups are equally distinct and in view of the marked

differences between their orientation and that of the hyoglossus muscle, they

will be described separately.

Extrinsic muscles

The m. hyoglossus (hg, Figs 9-12) is a paired longitudinal muscle, extending

parallel to the midline from the hyoid apparatus to the anterior tip of the tongue.

Posteriorly the muscle is dorsoventrally flattened and lies ventrolaterally to the

trachea and the oesophagus, laterally to the first ceratobranchial and dorso-

laterally to the posterior part of the geniohyoideus muscle. Anteriorly it becomes

cylindrical, turning dorsally to the undersurface of the tongue to lie laterally

to the lingual process of the hyoid, medially to the geniohyoideus muscle,

and ventrolaterally to the glottis. It is sheathed by fibres of the vertical intrinsic

musculature. The most anterior part of the muscle lies dorsomedially to the

genioglossus muscle, and tapers towards the jaw symphysis to terminate ven-

trally to the anterior tip of the tongue.

196 ANNALS OF THE SOUTH AFRICAN MUSEUM

The muscle arises superficially in the throat region from the anterior

surface of the first ceratobranchial, medially to the origin of the geniohyoideus

lateralis muscle, ventrolaterally to the oesophagus and dorsolaterally to the

origin of the geniohyoideus medialis muscle. It inserts fleshily along the ventral

surface of the tongue, between the medial and lateral vertical fibres of the

intrinsic musculature and medially to the insertion of the genioglossus muscle.

The muscle is innervated by a branch of the hypoglossal nerve.

The m. genioglossus (ggl, Figs 9-12) is a paired muscle, lying laterally to

the ventral midline and extending from the jaw symphysis to the posterior

border of the tongue. In front it lies dorsolaterally to the geniohyoideus medialis

muscle, ventrolaterally to the hyoglossus muscle, and medially to the sublingual

gland. At the back the muscle extends laterally around the ventral surface of

the sublingual gland and behind it the fibres lie ventrally to the lateral margin

of the oral membrane. A small cylindrical group of fibres separates antero-

ventrally from the genioglossus muscle and extends posteriorly, lying ventro-

medially to the genioglossus muscle and dorsally to the geniohyoideus medialis

muscle. In line with the glottis the fibres of this bundle become confluent with

those of the geniohyoideus medialis muscle. It is innervated by a minute ramus

branching from the hypoglossal nerve.

The genioglossus arises tendinously at the jaw symphysis, taking origin

from the inner ventral surface of the dentary immediately lateral to the sym-

physis, from the connective tissue surrounding the symphysis and, in the mid-

line, from the sheet of fascia covering the throat musculature ventrally. It inserts

along the ventral surface of the tongue, laterally to the hyoglossus muscle

and the lateral group of vertical intrinsic fibres, and interlaces with the transverse

fibres of the intrinsic musculature. The muscle is innervated by a branch of the

hypoglossal nerve.

Intrinsic musculature

The intrinsic muscles are innervated by the hypoglossal nerve and consist

of three groups of fibres, i.e. the vertical lingual, the longitudinal lingual and

the transverse lingual fibres, and although they interweave to some extent each

group remains distinct.

The m. verticalis linguae (vl, Figs 9-11) consists of a superior and an

inferior group of fibres. The superior fibres lie dorsally to the transverse lingual

muscle and form the papillae of the tongue. The inferior fibres lie ventrally

to the transverse lingual muscle, interlace with its fibres, and extend from the

apex of the tongue to the glottis. These fibres consist of a medial and a lateral

group. The lateral group lies between the genioglossus and the hyoglossus

muscles while the medial group lies between the hyoglossus muscle and the mid-

line. The two groups meet tendinously ventral to the hyoglossus muscle.

The m. transversalis linguae (tl, Figs 9-11) lies between the inferior and

superior vertical fibres. Its fibres extend across the width of the tongue from

the apex to the roots and interlace with the fibres of the inferior vertical, the

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 197

hyoglossus and the genioglossus muscles.

The m. longitudinalis linguae (Il, Figs 9-10) lies ventrally along the rim

of the tongue, laterally to the insertion of the genioglossus muscle on either

side. It extends from behind the apex of the tongue to nearly in line with the

glottis as a single cylindrical bundle of fibres, breaking up into smaller bundles

posteriorly and becoming obscured by the insertion of the genioglossus muscle.

The m. geniohyoideus lateralis (ghl, Fig. 12) is a narrow muscle extending

between the ventral surface of the jaw and the hyoid apparatus. It lies ventro-

medially to the jaw, ventrolaterally to the genioglossus muscle, deep to the

intermandibularis posterior muscle, and ventrally to the ‘Kauwulst’ of the

pterygoideus muscle.

It arises fleshily on the ventral surface of the jaw from a short distance

behind the symphysis to the posterior mylohyoid foramen. The origin consists

of five successive bundles of longitudinal fibres interlacing with the fibres of

the intermandibularis anterior muscle. The muscle inserts on the anterolateral

tip of the sole remaining posterior prong of the hyoid apparatus (usually

taken to be the first ceratobranchial). The insertion is fleshy and lies lateral

to that of the geniohyoideus medialis and hyoglossus muscles. The muscle is

innervated by a branch of the glossopharyngeal nerve.

The m. geniohyoideus medialis (ghm, Figs 9-12) is a superficial group

of fibres extending from the anteroventral surface of the genioglossus muscle

to the hyoid apparatus. The muscle lies laterally to the ventral midline, deep

to the intermandibularis musculature, ventromedially to the genioglossus

muscle and below the bundle of fibres extending between it and the genio-

glossus muscle. Posteriorly the muscle is flattened dorsoventrally and lies

ventromedially to the hyoglossus muscle, deep to the intermandibularis

posterior muscle and medially to the hypoglossal nerve. Anteriorly the muscle

becomes triangular in cross section and lies deep to the intermandibularis

anterior muscle.

The muscle arises tendinously behind the origin of the genioglossus

muscle, from the deep surface of the sheet of fascia covering the throat muscula-

ture ventrally and inserts fleshily along the ventrai surface of the first cerato-

branchial, ventromedially to the origin of the hyoglossus muscle. The muscle

is innervated by a branch of the glossopharyngeal nerve.

Depressor mandibulae group

The m. depressor mandibulae (Figs 14-16) is a superficial sheet of fibres

behind the adductor musculature. It lies laterally to the stapedial artery, the

lateral head vein and the hyomandibular ramus of VII. On its ventrolateral

surface it is obliquely overlain by the prominent cervicomandibularis muscle

which in its turn is covered by the dorsoventral fibres of the sheet-like constrictor

colli muscle. There is no indication in either Typhlosaurus aurantiacus or Acontias

meleagris that the depressor mandibulae and cervicomandibularis muscles

are continuous,

198 ANNALS OF THE SOUTH AFRICAN MUSEUM

PAR

GHL

Fig. 14. Cross-section of the skull at the level of the stapes.

The depressor mandibulae consists of an anterior portion arising cranially

and & posterior portion arising cervically. The anterior portion (dma, Figs 7,

14-15) is spindle-shaped and lies immediately behind the stapes. It arises fleshily

from the anterolateral surface of the fused exoccipital-opisthotic bone, postero-

dorsally to the quadrate head, and extends vertically downwards, laterally to

the posterior half of the stapedial footplate, to insert fleshily on the dorsal

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 199

Imm

Sc SS

7S Oy LS

(Ole

EGE

Ce \

ms :

IT colle)

ip)

a0 ES)

Hh Oo

Fig. 15. Cross-section of the skull at the level of the anterior portion of the depressor

mandibulae.

surface of the retro-articular process behind the tendon connecting the stapes to

the mandible.

The posterior portion (dmp, Fig. 16), a thin triangular sheet of fibres

lateral to the obliquus capitis magnus muscle and the innervations of the longis-

200 ANNALS OF THE SOUTH AFRICAN MUSEUM

simus and episternocleidomastoideus muscles, lies against the posterior border

of the cranial portion of the depressor mandibulae. It arises along the insertional

tendon of the longissimus cervicis muscle, ventrolateral to the spinalis capitis

Fig. 16. Cross-section of the skull at the level of the posterior portion of the depressor

mandibulae.

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 201

muscle and between the origin of the cervicomandibularis muscle and the

posterodorsal border of the adductor mandibulae musculature. The fibres

converge anteroventrally to insert behind those of the cranial portion by means

of a small tendon on to the posterodorsal extremity of the retro-articular process

of the mandible.

The depressor mandibulae is innervated by the hyoid ramus of VII, which

branches off behind the stapedial footplate from the hyomandibular ramus,

pierces the medial surface of the muscle and courses anteriorly for a short

distance within it.

The m. cervicomandibularis (cm, Figs 6—7, 16) is a large elongated sheet

of fibres medial to the constrictor colli muscle. It extends antero-ventrally,

superficial to the cervical musculature, from the level of the seventh dorsal

vertebra to the anteroventral surface of the jaw. It lies lateral to the episterno-

cleidomastoideus muscle, the longissimus cervicis and capitis muscles, and the

anterior parts of the iliocostalis system and the oblique hypaxial muscles.

The muscle arises fleshily from the anterolateral surface of the iliocostalis

system and the oblique hypaxial muscles, from the longissimus cervicis muscle,

and along its border from the dorsal intermuscular septum. Its fibres extend

forward only as far as the posterolateral surface of the ‘Kauwulst’ of the ptery-

goideus muscle where they attach to a thin sheet of fascia which covers the

‘Kauwulst’ laterally and ventrally and lies superficial to the throat muscles.

Anteriorly the tendon becomes aponeurotic and inserts along the ventral

surface of the jaw, from the anterior border of the posterior intermandibular

muscle to just lateral to the symphysis.

The m. cervicomandibularis is innervated by a branch of VII which pierces

the medial surface of the muscle in line with the occipital condyle of the

skull.

The m. constrictor colli (cc, Figs 5, 15-16) is a thin superficial sheet of

fibres covering the cervical region immediately below the skin. Its fibres extend

anteroventrally from the cervical region to cover the pterygoideus muscle

posterolaterally and the cervicomandibularis muscle anteroventrally. The

muscle is triangular in lateral aspect and its anterior border lies immediately

behind the extracolumella. The upper border of the muscle tapers postero-

ventrally and it terminates at a point ventrolateral to and approximately in

line with the third vertebra.

The muscle arises fleshily from a thin superficial sheet of cervical fascia

extending ventrally from the dorsal intermuscular septum, situated between the

transversospinalis and longissimus systems, to insert ventrolaterally in the

cervical region on to a superficial sheet of fascia covering the throat from the

jaw symphysis posteriorly to the rectus abdominis muscles.

The muscle is innervated by a branch of the hyomandibular ramus of VII

which passes through the cervicomandibularis muscle to enter the deep surface

of the constrictor colli in line with the posterior border of the condyle of the

skull.

202 ANNALS OF THE SOUTH AFRICAN MUSEUM

Cervical musculature

In contrast to non-fossorial lizards, the cervical extensor and flexor muscles

in Typhlosaurus aurantiacus play an active role during locomotion and especially

during burrowing movements. However, in spite of this added function the

distribution of the individual muscles retains a pattern common to saurians in

general.

The nuchal ligament is a vertical mid-dorsal sheet in the cervical region

extending from the occiput to the neural spine of the axis. Dorsally the ligament

is continuous with the fascia covering the transversospinalis system. This

fascia is laterally continuous with the dorsal intermuscular septum lying between

the transversosponalis and longissimus systems.

The m. spinalis capitis (sc, Figs 6, 12, 14-16) is a flat, dorsally situated

muscle extending immediately below the skin from the level of the twelfth

vertebra to the occiput. It lies lateral to the nuchal ligament and dorso-medial

to the anterior part of the longissimus dorsi muscle and its cervical derivative,

the longissimus cervicis. The muscle covers the rectus capitis anterior and

obliquus capitis magnus muscles. The lateral fibres arise fleshily from the

lateral margin of the dorsal intermuscular system.

The fibres insert tendinously on to the posterodorsal surface of the parietal

bone. The insertion is confined to a shallow depression on the parietal anterior

to the supra-occipital-parietal suture and lateral to the small mid-dorsal ridge

formed by the ascending process of the tectum synoticum.

The muscle is innervated by a branch of the dorsal ramus of the first

spinal nerve which passes between the rectus capitis posterior and the obliquus

capitis magnus muscles.

The m. rectus capitis posterior and the m. obliquus capitis magnus are

partially fused and appear as a single group of fibres. However, in the interests

of clarity they will be described separately.

The m. rectus capitis posterior (rp, Figs 6, 8) extends from the atlas to

the occiput. It lies ventral to the spinalis capitis muscle, lateral to the nuchal

ligament, dorso-medial to the longissimus cervicis muscle and antero-medial

to the obliquus capitis magnus muscle, which arises posterior to it. In Typhlo-

saurus aurantiacus the rectus capitis posterior is a single muscle and it probably

represents the fused rectus capitis superficialis and profundus muscles still

present, although partially fused, in such forms as Jguana iguana (Olson 1936).

The rectus capitis posterior muscle can be distinguished from the obliquus

capitis magnus muscle by the passage of the dorsal ramus of the first spinal

nerve between them as in Ctenosaura pectinata (Oelrich 1956).

The muscle arises fleshily from the lateral surface of the axial neural arch

and the aponeurotic fascia covering the atlanto-occipital gap. Some fibres also

arise from the dorsal surface of the obliquus capitis magnus muscle.

The fibres insert fleshily, deep to the spinalis capitis muscle and dorso-

medial to the insertion of the obliquus capitis magnus muscle, on to the dorsal

surface of the supraoccipital bone and that part of the fused exoccipital-

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 203

opisthotic bone dorsal to the ridge formed by the lateral semicircular canal

of the internal ear.

The muscle is innervated by a branch of the dorsal ramus of the first

spinal nerve.

The m. obliquus capitis magnus (oc, Figs 6, 8) extends from the fifth

vertebra to the lateral margin of the fused exoccipital-opisthotic bone. It lies

ventral to the spinalis capitis muscle, posterolateral to the rectus capitis posterior

muscle, dorsal to the anterior part of the spinalis dorsi muscle, dorsal to the

rectus capitis anterior muscle and medial to the longissimus cervicus muscle.

It arises fleshily from the dorsal extremities of the neural spines of the

third, fourth and fifth vertebrae, the tendinous tissue connecting the spines

and from the fascia covering the spinalis dorsi muscle.

The fibres extend obliquely forward and insert tendinously on to the

lateral margin of the fused exoccipital-opisthotic bone, attaching to the ridge

formed by the lateral semicircular canal of the internal ear, ventrolateral

to the rectus capitis posterior muscle and dorsomedial to the insertion of the

longissimus cervicis muscle.

The muscle is innervated by the dorsal ramus of the first spinal nerve.

The m. longissimus dorsi lies ventrolateral to the transversospinalis system

and dorsal to the heads of the ribs. At the level of the fourth vertebra it divides

into a dorsal and a ventral group of fibres. The dorsal group, the m. longissimus

cervicis (Ice, Figs 6-8) lies ventrolateral to the spinalis capitis and rectus capitis

posterior muscles and lateral to the obliquus capitis magnus muscle. The

muscle arises fleshily approximately from the level of the seventh to the second

vertebrae from the fibres of the longissimus dorsi muscle. It extends anteriorly

dorsal to the longissimus capitis muscle and lateral to the obliquus capitis

magnus muscle, to insert tendinously on to the lateral margin of the fused

exoccipital-opisthotic bone, lateral to the insertion of the obliquus capitis

magnus muscle and medial to the insertion of the episternocleidmastoideus

muscle.

The muscle is innervated by the dorsal ramus of the first spinal nerve.

The ventral group of fibres, the m. longissimus capitis (Ica, Fig. 8), extends

anteroventrally from the level of the fourth vertebra to the basal tuberosity

of the basi-occipital bone. It lies ventral to the longissimus cervicus muscle,

medial to the episternocleidomastoideus muscle, dorsolateral to the longus

colli muscle and lateral to the rectus capitis anterior muscle. The fibres arise

fleshily from the longissimus dorsi muscle and the synapophysis of the first

four vertebrae to insert tendinously on to the basal tuberosity lateral to insertion

of the rectus capitis anterior muscle and dorsomedial to the insertion of the

longus colli muscle.

The muscle is innervated by a branch of the dorsal ramus of the first

spinal nerve.

The m. rectus capitis anterior (ra, Fig. 8) is a group of short fibres extending

from the axis to the occiput. The muscle lies ventrolateral to the axis, the

204 ANNALS OF THE SOUTH AFRICAN MUSEUM

atlas and the occipital condyle of the skull; medial to the longissimus capitis

muscle and dorsal to the anterior part of the longus colli muscle with which

some of its ventral fibres are confluent.

It arises fleshily on the ventrolateral surface of the axis medial to the

synapophysis and ventrolaterally on the atlas. The fibres insert fleshily on to

the basioccipital and exoccipital-opisthotic bones. The insertion lies ventral

to the insertion of the rectus capitis posterior muscle, dorsal to the insertion

of the longus colli muscle and dorsomedial to the insertion of the longissimus

capitis muscle.

The muscle is innervated by a branch of the first spinal nerve.

Fig. 17. Camera lucida drawing of the left lower jaw; lingual view.

DISCUSSION AND CONCLUSIONS

General

The morphology of fossorial skinks in general is paralleled by that of

snakes in many ways and it is therefore interesting to note that according to the

theory of Walls (1942) snakes originated as fossorial forms. Any evaluation of

the musculature of Typhlosaurus aurantiacus must be made in the light of the

fact that the animal leads a predominantly subterranean existence which does

not involve the construction of burrows. Huey er al. (1974) describes Typhlo-

saurus as a sand swimming lizard which normally moves in a lateral sinuous

path beneath the sand. 7. aurantiacus has a subterminal mouth as in other

fossorial lizards, e.g. Acontias. The position of the mouth prevents soil particles

from entering the buccal cavity during burrowing movements. De Weerdt

(1971) indicates that it is important to a fossorial lizard like Dibamus to use

its mouth in a terminal position. This argument is based on the assumption

that the lizard lives in a burrow and encounters its prey directly in front of it.

Neither Typhlosaurus nor probably Dibamus lives in a burrow and conse-

quently prey may be approached from any angle.

The animal uses its head as a burrowing tool, and the skull and its associ-

ated musculature are consequently strongly modified. Temporal arches and

posttemporal fenestrae are absent. The elongated temporal region is strengthened

by the lateral downgrowth of the parietal and the broad anterior superior

processes of the pro-otic. These structures also serve as areas of origin to the

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 205

adductor musculature. The occipital region is strengthened by the fused exoccipi-

tal and ophisthotic bones and the expanded nature of the occiput allows the

cervical musculature to insert relatively far forward on to the skull.

As in Dibamus (Gasc 1968) Typhlosaurus aurantiacus lacks a m. levator

bulbi. This condition is probably associated with the degeneration of the

eyes. According to Haas (1973) the structural diversity of the m. levator bulbi

in lizards appears not to be controlled by phylogenetic factors but rather by

functional factors such as the presence or absence of a movable lower eyelid

or a general reduction of the visual apparatus.

The m. pseudotemporalis is single in Typhlosaurus aurantiacus as in the

Gekkonidae, the Pygopodidae and the snakes. De Weerdt (1971) describes a

single m. pseudotemporalis in Dibamus but fails to define the position of the

muscle in relation to the maxillary ramus of V. It may well be that the muscle is

in fact part of the m. adductor mandibularis externus. Gasc (1968) describes

am. pseudotemporalis in Dibamus consisting of two parts. Haas (1973) interprets

Gasc’s description as pertaining only to the posterior of the two portions.

However, Gasc, on page 135, clearly states that: ‘Une nappe profonde (fig. 9)

formée par deux chefs. . . . Cette nappe pourrait correspondre, d’aprés ses

insertions, aux deux chefs du m. adductor mandibularis medius (= pseudo-

temporalis); toutefois, la branche maxillaire du trijumeau passe ici au-dessous

de ce plan musculaire.’ From Gasc’s figure 9 it is clear that the maxillary ramus

of V lies medial to the m. pseudotemporalis. It is probable therefore that this

muscle forms part of the m. adductor mandibularis externus and not the m.

adductor mandibularis internus. According to Haas (1973) the gekkonids and

pygopodids lack the m. pseudotemporalis superficialis but retain the profundus

portion of the muscle which consists of an anterior and a posterior part. It

is probable that the single muscle retained in 7. aurantiacus represents the

profundus portion of the m. pseudotemporalis and that the reduction of the

m. pseudotemporalis in this animal is related to the loss of the temporal arches

as Haas (1973) believes it to be in the case of gekkonids, pygopodids and snakes.

The depressor mandibulae is a relatively small muscle and (in theory)

its position close to the fulcrum of the jaw is not functionally optimal. Since

the opening of the jaw is usually assisted by gravity this condition is not a

liability. However, in a lizard which feeds subterraneously the surrounding

pressure of the soil may demand a more sophisticated arrangement of the jaw

opening muscles. In Typhlosaurus aurantiacus the cervicomandibularis is

probably the main jaw opening muscle since its origin on the neck musculature

and ventral insertion on the jaw makes it ideally suited for this purpose. Camp

(1923) notes that the cervicomandibularis muscle is enormously developed in

all burrowers.

From the forwardly extended insertion of the cervical musculature on to

the occiput and the lateral extension of the synapophyses of the axis and the

three following vertebrae it is evident that this group of muscles plays an

important role in locomotion. It serves to flex and extend the skull as well as

206 ANNALS OF THE SOUTH AKRICAN MUSEUM

stiffen the atlanto-occipital joint during burrowing. The degree of fusion

between individual cervical muscles seems logical in the light of their function.

Cranial kinesis

Versluys (1910, 1912) described the movable joints of the reptilian skull.

He divided the skull into an ‘occipital segment’ consisting of the bones of the

braincase and the parasphenoid, and a ‘maxillary segment’ comprising the rest

of the skull. The intracranial movements between the two segments are known

as kinesis and were interpreted by Versluys as a mechanism for increasing the

gape of the mouth by lifting the snout. Various degrees of kineticism exist,

and skulls ranging from akinetic, with little or no movement between the

‘segments’, to amphikinetic, in which more than two movable parts are found.

The constrictor dorsalis group of muscles is responsible for the kinetic move-

ments of the skull.

Versluys based his conclusions on morphological studies, but recent workers

have made use of sophisticated methods to study live material. Frazetta (1962)

who revised Versluys’s terminology, used motion pictures to record the capture

of prey as well as electrical stimulation and biomechanical analysis of the

muscles. Iordansky (1970) used biomechanical analysis to extend the approach

of Frazetta. In contrast to Versluys, Frazetta concluded that kinesis actually

lessens oral gape. However, in spite of the advanced techniques employed by

them, Frazetta and Iordansky are not in full agreement on certain aspects of

kinesis.

It is evident that kinesis is a complex mechanism of which the functional

significance is not yet fully explained. This is also clear from the variable nature

of the constrictor dorsalis group of muscles in a form such as Sphenodon.

Frazetta (1962) describes Sphenodon as akinetic whereas Ostrom (1962) describes

a specimen which has both a levator pterygoidei and a protractor pterygoidei

muscle. According to Ostrom, in previously described specimens of Sphenodon

either one of these muscles were present but never both. The study of cranial

Kinesis therefore requires the application of sophisticated techniques to live

specimens as well as the dissections of numerous examples of the same species.

The scope of this paper and the paucity of material precludes an in-depth

study of cranial kinesis in Typhlosaurus aurantiacus but, since the cranial

muscles have been described in detail, a brief summary will be given here.

According to Bellairs (1969) fossorial lizards tend to become monokinetic

or even akinetic. A reduction of intracranial movements seems logical in the

light of strengthening the skull for burrowing. Usually it appears that the

metakinetic bending plane between the supraoccipital and parietal bones is

reduced in favour of the mesokinetic bending plane between the parietal and

frontal bones as in Acontias (De Villiers 1939, Brock 1941, Van der Merwe

1944); Monopeltis capensis (Kritzinger 1946); Anniella (Toerien 1950, Bellairs

1969); Nessia (Bellairs 1969) and Dibamus (De Weerdt 1971). According to

Leonard (1973) the less specialized burrowing skink Sce/otes is amphikinetic.

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 207

In Typhlosaurus the presence of a small levator pterygoidei muscle, a

substantial protractor pterygoidei muscle, a synovial articulation between

the quadrate and the skull and a movable basipterygoid articulation clearly

indicate a certain amount of intracranial movement. Because of the posterior

expansion of the skull, the occipital bones have become fused and the insertional

areas of the cervical musculature have increased to such an extent that the

spinalis capitis muscle inserts dorsally on the posterior part of the parietal,

anterior to the position of the metakinetic bending plane.

The position of this muscle suggests a sharp reduction, if not total absence,

of a functional metakinetic bending plane, despite the presence of the carti-

laginous ascending process of the tectum synoticum. The post-orbital bar is

incomplete and according to Leonard (1973) this is a prerequisite for meso-

kinesis. Smit (1964) agrees that metakinesis is reduced or absent and states

that movement is clearly possible between the parietal and the frontal bones,

indicating that the 7yphlosaurus skull is definitely mesokinetic.

Jaw mechanics

According to Ostrom (1964) the vertebrate lower jaw operates as a lever

of the third class during adduction. This arrangement ensures maximum

depression of the jaws with a minimum length of adductor muscle fibres.

In a system of this kind the mechanical advantage is directly proportional

to the length of the moment arm if the applied force (adductor musculature)

remains constant. The moment arm is defined as the perpendicular distance

between the line of applied force and the fulcrum (Fig. 18A). In the jaw the

moment arm represents the distance between the jaw articulation and the tip

of the coronoid process.

If the line of applied force functions in a posterior direction, at an angle

of less than ninety degrees to the long axis of the lever, the moment arm FB

(Fig. 18A) is no longer perpendicular to the applied force and is effectively

displaced to position FB’ (Fig. 18B) with the result that the length of the moment

arm is decreased and the system functions at a disadvantage. However, this

condition can be overcome by raising the point of attachment (development

of a coronoid process) of the applied force (Fig. 18C).

From Figure 18C it follows that: m? = x? + y?.

The moment arm (m) is therefore a function of x (the distance between

the coronoid process and the jaw articulation) and y (the height of the coronoid

process). If y is constant x will determine the line of muscle action (@) and vice

versa, because tan 0 — >.

Consequently, with y constant any decrease in x will result in a more

posteriorly directed line of muscle action, or, alternatively, an increase in x

will result in a more perpendicular orientation of the adductor fibres. If x is

kept constant and y decreased the fibre orientation would become more vertical

208 ANNALS OF THE SOUTH AFRICAN MUSEUM

Fig. 18. Diagram to illustrate the action of the lower jaw.

and if y is increased the fibre orientation would become more posteriorly

directed. It is clear therefore that the coronoid process in terms of height (y)

and distance from the articulation (x) is functionally important in determining

the action of the lower jaws and its associated musculature, and not as De

Weerdt (1971) suggests, mainly a strengthening device.

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS 209

The vertebrate lower jaw, seen in terms of the mechanics of a third class

lever, would theoretically function at optimal efficiency with the adductor

fibres orientated perpendicular to the long axis of the lower jaw and inserted

on to the jaw as close as possible to the symphysis.

Ostrom (1964) notes two disadvantages in this arrangement. As a result

of increasing x the gape of the mouth will correspondingly decrease. However,

De Mar & Barghusen (1973: 626) state: ‘If the increase in relative lengths

of the moment arms achieved by increasing y and increasing x are the same,

the increase in distance that the muscle must stretch to achieve a given gape

is the same for the two methods. Thus . . . reduction of gape is the same and

not a consideration per se in making the comparison.’

Secondly, Ostrom (1964) indicates that because of their vertical orientation

the origin of the adductor fibres would encroach on to the facial region, restrict-

ing their size and power. This statement is true except in cases where the orbit

is anteriorly placed or decreased in size, making it possible to extend the tem-

poral origin of the jaw adductors anteriorly. In Typhlosaurus the eye is degenerate

and lacks eye muscles. The orbit is consequently reduced and the temporal

region elongated. The lateral downgrowth of the parietal and the forward

extension of the anterior superior process of the pro-otic makes additional

areas of origin available for the adductor musculature, compensating for the

loss of such structures as the supratemporal arch. The relatively forward

position, therefore, of the adductor muscles suggests a difference in the line

of muscle action as compared to a non-fossorial skink like Mabuia.

From the work of De Mar & Barghusen (1973) it is clear that the height

and position of the coronoid process is influenced by the line of muscle action.

Any difference, therefore, in the line of muscle action would be reflected in

the proportions of the lower jaw.

In comparing the lower jaws of Typhlosaurus and Mabuia the outstanding

feature is their proportional similarity in terms of x and y. The tooth row,

however, is shorter in Typhlosaurus than in Mabuia because of the subterminal

mouth of the former. Consequently, the force of the bite at the jaw symphysis

will probably be proportionately greater in Typhlosaurus than in Mabuia. The

similarity of the two lower jaws suggests that the mean line of muscle action

is identical in both forms, and that there is probably no difference of any

consequence in the action of the jaw.

It therefore appears that the primary adaptation for a fossorial habit is

streamlining of the body and its various parts. Loss of limbs and attenuation

of the body is associated with the new mode of locomotion. Strengthening

of the skull for burrowing results in the lateral downgrowth of the parietal

bone and the extension of the anterior superior process of the pro-otic bone,

the lengthening of the temporal region, and the loss of metakinesis and the

supratemporal arch.

It may be concluded therefore that the distribution of the jaw muscles

in Typhlosaurus represents the optimal functional arrangement to maintain a

210 ANNALS OF THE SOUTH AFRICAN MUSEUM

mode of jaw action essentially similar to that of a non-fossorial lizard such as

Mabuia capensis, within a skull that is proportionally different because of

marked changes resulting from a fossorial mode of life.

ACKNOWLEDGEMENTS

I wish to thank the following persons: Professor M. E. Malan of the

Zoological Institute of the University of Stellenbosch, who suggested the

project, for her guidance and assistance during the research; Dr M.A. Cluver

of the South African Museum for critically reading the manuscript; Messrs

M. N. Bester, A. J. Lindvelt, D. J. van Eeden, D. P. Mostert and Mrs

R. Semmellink, all of the Zoological Institute at Stellenbosch for assistance

rendered at various stages of the work; Mrs I. Chesselet of the South African

Museum, her family and Mr P. J. Louw of Klein Botrivier for their fieldwork;

Mr N. J. Eden of the South African Museum for taking the photographs;

Miss A. E. Louw and Mrs P. D. Eedes for helping with the typing, and my wife

Lorna for her valued assistance.

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*Not seen in the original.

CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANTIACUS

ABBREVIATIONS

anterior process of the coronoid

m. adductor mandibulae externus medius

m. adductor mandibulae externus profundus

m. adductor mandibulae externus superficialis

anterior inferior process of the pro-otic

m. adductor mandibulae posterior

articular

anterior superior process of the pro-otic

stapedial artery

bodenaponeurosis

buccal cavity

buccal lining

basioccipital

basipterygoid process

brain

basal tuberosity

coronoid

m. constrictor colli

internal carotid artery

m. cervicomandibularis

coronoid process

dentary

anterior portion of the m. depressor mandibulae

posterior portion of the m. depressor mandibulae

eye

m. episternocleidomastoideus

extracolumella

Gasserian ganglion

m. genioglossus

m. geniohyoideus lateralis

m. geniohyoideus medialis

groove for the insertion of the pseudotemporalis muscle

fascia supporting the extracolumella anteriorly

pad of fibrocartilage

foramen for the chorda tympani

m. hyoglossus

m. intermandibularis anterior

infraorbital fenestra

m. intermandibularis posterior

insertional tendon of the m. cervicomandibularis

insertional tendon of the m. pterygoideus

lateral lamina of the bodenaponeurosis

m. longus colli

m. longissimus capitis

m. longissimus cervicis

longitudinal lingual fibres

m. levator pterygoidei

lateral lamina of the quadrate tendon

lateral semicircular canal

lateral head vein

musculus

medial lamina of the bodenaponeurosis

Meckelian cartilage

medial lamina of the quadrate tendon

lateral mandibular shelf

nuchal ligament

m. obliquus capitis magnus

214 ANNALS OF THE SOUTH AFRICAN MUSEUM

oe fused ophistotic-exoccipital

p m. pseudotemporalis

pa _ pre-articular

pal palatine

par parietal

pat ascending process of the tectum synoticum

pb __ parasphenoid — basisphenoid

pe posterior process of the coronoid

pd tendinous pad on m. pterygoideus

pe lingual process

pf postfrontal

pm _ posterior mylohyoid foramen

pn palatine nerve

po pro-otic

prp m. protractor pterygoidei

pt pterygoid

pts m. pterygoideus

q quadrate

ga quadrate tendon

r rostral

ram. rectus capitis anterior

rm mandibular ramus of V

rma maxillary ramus of V

rop opthalmic ramus of V

rpm. rectus capitis posterior

S stapes

sa surangular

sc spinalis capitis

sd =m. spinalis dorsi

sp _ splenial

sq. squamosal

st supratemporal

t tendinous sheath of the extra columella

tc tendinous connection between supratemporal and quadrate

tl tranverse lingual fibres

to tongue

tr trachea

ts tendon between the squamosal and quadrate

vb vertical lamina of the bodenaponeurosis

vl vertical lingual fibres

vq vertical lamina of the quadrate tendon

6. SYSTEMATIC papers must conform with the International code of zoological nomenclature

(particularly Articles 22 and 51).

Names of new taxa, combinations, synonyms, etc., when used for the first time, must be

followed by the appropriate Latin (not English) abbreviation, e.g. gen. n., sp. n., comb. n.,

syn. n., etc.

An author’s name when cited must follow the name of the taxon without intervening

punctuation and not be abbreviated; if the year is added, a comma must separate author’s

name and year. The author’s name (and date, if cited) must be placed in parentheses if a

species or subspecies is transferred from its original genus. The name of a subsequent user of

a scientific name must be separated from the scientific name by a colon.

Synonymy arrangement should be according to chronology of names, i.e. all published

scientific names by which the species previously has been designated are listed in chronological

order, with all references to that name following in chronological order, e.g.:

Family Nuculanidae

Nuculana (Lembulus) bicuspidata (Gould, 1845)

Figs 14-15A

Nucula (Leda) bicuspidata Gould, 1845: 37.

Leda plicifera A. Adams, 1856: 50.

Laeda bicuspidata Hanley, 1859: 118, pl. 228 (fig. 73). Sowerby, 1871: pl. 2 (figs 8a—b).

Nucula largillierti Philippi, 1861: 87

Leda bicuspidata: Nicklés, 1950: 163, fig. 301; 1955: 110. Barnard, 1964: 234, figs 8-9

Note punctuation in the above example:

comma separates author’s name and year

semicolon separates more than one reference by the same author

full stop separates references by different authors

figures of plates are enclosed in parentheses to distinguish them from text-figures

dash, not comma separates consecutive numbers

Synonymy arrangement according to chronology of bibliographic references, whereby

the year is placed in front of each entry, and the synonym repeated in full for each entry, is

not acceptable.

In describing new species, one specimen must be designated as the holotype; other speci-

mens mentioned in the original description are to be designated paratypes; additional material

not regarded as paratypes should be listed separately. The complete data (registration number,

depository, description of specimen, locality, collector, date) of the holotype and paratypes

must be recorded, e.g.:

Holotype

SAM-—A13535 in the South African Museum, Cape Town. Adult female from mid-tide region, King’s Beach,

Port Elizabeth (33.51S, 25.39E), collected by A. Smith, 15 January 1973.

Note standard form of writing South African Museum registration numbers and of date.

7. SPECIAL HOUSE RULES

Capital initial letters

(a) The Figures, Maps and Tables of the paper when referred to in the text

e.g. “... the Figure depicting C. namacolus ..

*...in C. namacolus (Fig. 10)...’

(b) The prefixes of prefixed surnames in all languages, when used in the text, if not preceded

by initials or full names

e.g. Du Toit but <A. L. du Toit

Von Huene but: ~_F. von Huene

e.g. Therocephalia, but therocephalian

Punctuation should be loose, omitting all not strictly necessary

Reference to the author should be expressed in the third person

Roman numerals should be converted to arabic, except when forming part of the title of a

book or article, such as

“Revision of the Crustacea. Part VIII. The Amphipoda.’

Specific name must not stand alone, but be preceded by the generic name or its abbreviation

to initial capital letter, provided the same generic name is used consecutively.