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Show 220 DR. R. W. SHUFELDT ON [Apr. 1, vomers, and contribute largely to the osseous floor and inner wall either narial aperture in front. Parial vomers are found in the skull of Heloderma. They arc 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 iu 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 tuberculata, where they are in contact with each other, mesially, for their entire lengths ! Either 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 suturaily connected with the lacrymal, the os transversum, the maxillary, and the prefrontal. True fusion has almost taken place 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 hone 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 postfrontal 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, maxillary, and jugal bones, we find the small lacrgmal 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 bengalcnsis, as well as an imperfect skeleton of Crotuphutus collaris, both from the collections of the U . S. National Museum (Nos. 20226, 29151 respectively). |