1890.] HELODERMA SUSPECTUM. 161 



consists of a loosely connected plain of coarse fibres, which arise 

 from the outer half of the posterior cornua of the hyoid, from the 

 under surface of the anterior horn of the same bone, and from the 

 membrane of the floor of the mouth. Passing directly forwards it 

 inserts itself, tendinous, into the inner aspect of the dentary 

 element of the mandible posterior to tbe symphysis. From this it 

 will be seen that this muscle is posteriorly broad and anteriorly 

 narrow. 



10. Mandibularis. — This is a muscle that, thus far, ] have failed 

 to find any published description of, although it was evidently seen 

 by Fischer, who has presented us with an imperfect drawing of it, 

 and apparently left the muscle unnamed (see fig. 1, Taf. xcvii. 

 Bronn's ' Thier-Reichs,' Bd. vi., iii. Abth., 33 & 34 Lief. 1882). 

 When I say an imperfect figure, I mean that the muscle does not 

 interdigitate with the m. genio-hyoideus superjicialis as Fischer has 

 represented it, at least it does not in the several specimens of 

 Heloderma suspectum wherein I have examined it. The mandibu- 

 laris is a small muscle which has an origin for about half a centimetre 

 on the inner aspect of the dentary element of the mandibular ramus 

 just posterior to the point of attachment of the cerato-mnndibularis. 

 It is quadrilateral in form, and its fibres pass directly across the 

 inter-ramal space to meet the muscle of the opposite side, which it 

 does in a delicate fascia in the median line. It is deep to the 

 genio-hyoideus, and I have provisionally bestowed the above name 

 upon it, until its homologies are better known. 



11. Cerato-mandibularis.- — In this we have a muscle that appears 

 to represent but a little more than the differentiated external margin 

 of the genio-hyoideus. It arises, on either side, from the apex of 

 the posterior cornua of the hyoid bone, and its fibres taking on the 

 same direction as those of the genio-hyoideus, the muscle inserts 

 itself by a delicate tendon into the antero-internal aspect of the 

 mandible just posterior to the insertion of the genio-hyoideus, and 

 upon the same plane with it. This muscle is the cerato-mandibular 

 of Mivart, and, in part, the mylo-hyoideus of Sanders ; it being the 

 cerato-mandibula7-is of Hoffmann. 



12. The Omo-hyoideus is a handsomely developed muscle in this 

 lizard, arising for the most part from the anterior border of the 

 clavicle of the same side, and from the summit of the interclavicle, 

 and apparently by a single head. Its fibres form a flat band, which, 

 passing forwards and inwards, insert themselves into the posterior 

 surface of the basihyal, and the hinder margin of the corresponding 

 thyro-hyal for the inner two thirds of its length. Mesially it meets 

 the muscle of the opposite side for a limited distance in front, and 

 for the most part is superficial to the next two muscles to be de- 

 scribed. Externally it is overla})ped by the sterno-mastoideus, and 

 we note that passing obliquely across its middle a tendinous line is 

 to be seen, from the external, and at the same time the most anterior, 

 half of which its fibres are inclined to be more outwardly directed, 

 before making their insertion into the thyro-hyal. 



13. The Sterno-hyoideus is a much slenderer muscle than the last 



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