SKULLS OF CYNODONT REPTILES. 913 



of this foramen jngulare is the prootic hone, which appears to 

 have two foramina in it. The posterior I beHeve to be for 

 nerve viii., and the anterior for vii. Between the prootic and 

 the large alisphenoid is seen the opening for probably both the 

 2nd and 3rd branches of nerve v. _ Immediately below this 

 foramen, the prootic sends a sharp bony process upwards, inwards, 

 and forwards. Probably it lay on the inner side of the Gasseiian 

 ganglion. 



The basisphenoid is a large bone, along the front of which lies 

 the back part of the vomer. There is no orbito- sphenoid and no 

 presphenoid bone. 



The vomer passes from the basisphenoid to about the middle of 

 the hard palate. Along its dorsal surface ran the cartilaginous 

 cranial axis, against which the grooved upper surface of the vomer 

 fits. At the front of the vomer the median cartilage is ossified, 

 and the bone is apparently the homologue of the mammalian 

 mesethmoid. In the figure given of the median section the 

 prevomer {P.vo.) and the septomaxillary (^Smx.) are largely 

 hypothetical. 



Sesamodon and Mellnodon. 

 (PI. XLVI. figs. 3, 4, & 5, and text-figs. 179, 180.) 



These two allied genera, which are both unfortunately very 

 imperfectly known, stand at present by themselves some distance 

 apart from the other Cynodonts. Each genus is known only by 

 a single specimen, which in the case of Sesamodon browni is only 

 fair, a,nd in the case of Melinodon simws very poor. Still the interest 

 attaching to the specimeiLS is so very great that it is necessary to 

 figure them as fully as possible. 



Though the only known skull of Sesamodon broioni is very badly 

 weathered and considerably crushed, it is fortunately possible to 

 restore the external appearance with much certainty. In fact the 

 only points in the external anatomy that remain in doubt are the 

 articidar region, the middle of the occiput, and pai'ts of the jugal, 

 frontal, parietal, and squamosal bones. 



The premaxilla is not very satisfactorily preserved, but presents 

 no unusual features. 



The septomaxillary is apparently fairly similar to that of 

 Nyihosaurits, appearing on the face to a considerable extent. 



The maxilla is large and resembles to some extent that of 

 Trirachodon, while in other respects it is nearer to Nythosaurus. 

 The canine is relatively smaller than in either Trirachodon or 

 Nythosaurus, but is situated, as in Nythosaurus, far back from 

 the front of the bone. The molars, with the exception of the 1st 

 which is small, form a uniform series, and the maxillary bones are 

 much approximated in the molar region, as in Trirachodon. 



The nasal resembles on the whole that of Bauria. The nostril 

 is directed mainly forward and the nasal to some extent over- 

 hangs it. The bone is moderately broad thioughout its whole 



