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Show 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 hvoid, 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 the symphysis. From this it will be seen that this muscle is posteriorly broad and anteriorly narrow. J 10. Mandilularis.-This is a muscle that, thus far, I 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 superficialis as Fischer has represented it, at least it does not in the several specimens of Heloderma suspectum wherein I have examined it. The mandibulars 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-mandibularis. 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-mandibularis 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 described. Externally it is overlapped 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 |