18y0,] HELODERMA SUSPECTUM. 225 



subcylindrical form ; they articulate with the basihyal posterior to 

 the mesial heads of the anterior cornua. Curving backwards and 

 outwards, their hinder ends are tipped with cartilage, which latter 

 character reminds one of the thyro-hyals as seen in most birds — all 

 ordinary existing birds. It is only the anterior joints of the pos- 

 terior cornua of the hyoidean arches in this Lizard that ossify ; all 

 the remaining parts of the apparatus are cartilaginous, even in very 

 old specimens. 



From this brief description it will be seen that the hyoidean 

 arches in Heloderma simply add another pattern of these structures 

 to the various forms they assume among Lizards generally. Ac- 

 cording to Cuvier, Hoffmann, the Parker, and many other anato- 

 mists, these parts differ in a number of species of the Geckos, in 

 Go?iyocephalus, in Iguana, in Sciiicus, in Chatnceleon, and iu many 

 other species and genera. 



Li such a species as Lacerta viridis, according to Professor T. J. 

 Parker (' Zootomy '), all three cornua of the hyoid apparatus are 

 present, the anterior, middle, and posterior, and such elements are 

 represented as the hypo-hyal, the stylo-hyal, the cerato-hyal, and 

 the epibranchial of the second branchial arch. 



On the Shoulder- Girdle and the Pectoral Limb. 



A description of the simple form assumed by the sternum in 

 Heloderma has already been presented above. This structural 

 simplicity appears to be extended to the shoulder-girdle. A broad 

 part of the mesial border of either coracoid remains cartilaginous, 

 and this is wider in front than it is behind. Fusing with the 

 corresponding scapula, the osseous part of the coracoid at a point 

 upon the posterior margin of the girdle yields to the articular 

 surface of the glenoid cavity its ventral moiety. Just anterior to 

 this point is to be seen a small fenestra, that appears to indicate the 

 original divisional space between the precoracoid and the coracoid 

 proper. In rough outline the form of the coracoid simulates the 

 sector of a circle, the apex being at the glenoid cavity. Anteriorly 

 these bones overlap each other, wliile posteriorly the mesial margin 

 of either one articulates with the groove occupying the antero- 

 external border of the sternum. In a specimen before me it is the 

 left coracoid that underlaps the right, while the clavicles and inter- 

 clavicle tend to hold them in this position. It may not, however, 

 be that the left bone is always positioned ventrad. From all this 

 it will be observed that the coracoid in Heloderma having the form 

 described, its several elements are so fused together that it remains 

 only to make out the cartilaginous epicoracoid (mesial rim), the 

 precoracoid and coracoid proper being indicated by the position of a 

 small foramen only, while the mesocoracoid, if it ever exists as a 

 separate ossification in this reptile, is here now completely co-ossified 

 with the other elements. 



Being rather less than one third the size of the coracoidal portion 

 of the girdle, the scapula has its upper and lower extremities dilated, 



[79J 



