220 DR. R. W. SHUFELDT ON [Apr. 1, 



vomers, and contribute largely to the osseous floor and inner wall of 

 either narial aperture in front. 



Parial vomers are found in the skull of Heloderma. They are 

 represented by rather long stout ossifications ; subcylindrical in 

 form, and either one showing a partial groove down its dorsal 

 aspect longitudinally. A septomaxillary notches a vomer on the 

 same side, externally, near its anterior end. These vomers are in 

 contact in front, but they gradually diverge from each other as they 

 pass backwards to articulate with the palatine of either side. How 

 different these bones are from the broad, flat vomers as we find them 

 in Iguana tiiberculata, where they are in contact with each other, 

 mesially, for their entire lengths ! 



YAihev jugal is represented by a strong curved bone which forms 

 the postero-ventral boundary of the external periphery of the orbit. 

 Behind it articulates with the postfrontal, while anteriorly it is 

 suturally connected with the lacrymal, the os transversum, the 

 maxillary, and the prefrontal. True fusion has almost taken [dace 

 among some of these sutures, notably the anterior ones. At its 

 postero-inferior angle behind, the jugal develops a stumpy apophysis. 

 Essentially this bone is a very different affair from what we find in 

 a Varanus, wherein it is reduced to almost spiculiform proportions 

 and curving upwards fails to reach the postfrontal ^ 



Making extensive articulations by very firm sutures with the 

 parietal, the prefrontal and frontal, and the jugal, a postfrontal 

 bone is here a fair-sized ossification that forms the supero-posterior 

 angle of the orbit, and completes the corresponding part of its 

 periphery. Instead of being a small and comparatively unimportant 

 bone, as indeed it is in some of the Lacertilians, the prefrontal in 

 Heloderma constitutes one of the most essential elements at the 

 fore part of the cranium. It is in sutural contact with the post- 

 frontal and frontal, with the nasal and the lacrymal, with the jugal, 

 the palatine, and finally with the maxillary. With the lacrymal it 

 forms the anterior wall of the orbit, as well as its antero-superior 

 margin. Internally, it bounds the lacrymal foramen, while its dorsal 

 surface is largely covered by a lateral extension of the co-ossified 

 dermal tubercles. 



Forming the outer boundary of the osseous lacrymal duct or 

 canal, and wedged in between or rather among the prefrontal, max- 

 illary, and jugal bones, we find the small lacrymal ossification. 

 Externally it is generally covered by one of the dermal ossifications 

 that overlie the surface of the skull in front, and it fuses with it. 



A palatine is seen to be a large tripronged bone that develops 

 a transverse ridge upon its dorsal aspect. This ridge articulates 

 with the prefrontal bone. The inner fork of the palatine articulates 

 with the hinder end of the vomer of the same side ; its posterior 

 fork engages the antero-internal limb of the corresponding pterygoid ; 



1 My thanks are due to Mr. F. A. Lucas for the loan of a skull of a specimen 

 of Varanus bengalensis, as well as an imperfect skeleton of Crotaphytus coUaris, 

 both from the collections of the U. S. National Museum (Nos. 29226, 29151 

 respectively). 



[74] 



