396 Miscellaneous. 



The occipital condyle is single, as is also the vomer, which forms 

 no part of the bony palate. 



The majority of the Saurian characters, in reference to existing 

 reptiles, of the skull are Lacertian, as indicated in the foregoing 

 description. 



The complex, extensive and well-ossified structure of the back 

 part of the cranium is similar to that in the Crocodile ; but as this 

 is an adaptation rather than a typical conformation, it affords but a 

 slender argument for their affinity, and the plan of structure, with 

 such varieties as do exist, is rather Lacertian. The occipital ex- 

 panse and strength depend in both the Crocodile and Ichthyosaur 

 on the necessity for a due extent of surface for the implantation of 

 the powerful nuchal muscles which must have mainly wielded a head 

 destined to overcome the resistance of the watery element in the 

 swift subaqueous course of the Ichthyosaur, and of a head produced 

 anteriorly into long and heavy jaws beset with numerous teeth. 



The fixation of the tympanic, the posterior position of the orbits, 

 the position and proportions of the temporal fossae, and the absence 

 of parietal hypapophyses on the basi-occipital, are Crocodilian cha- 

 racters. 



The median division of both parietal and frontal, the division of 

 the postfrontal, or superaddition of the postorbital, the meeting of 

 the post- and pre-frontals above the orbit, are characters met with 

 in some existing Lizards, as well in Labyrinthodonts. 



The huge orbits, the very long nasal and premaxillaries, the very 

 short and small frontals and maxillaries, the long continuous groove 

 for the loose insertion of the teeth, the shortness but great vertical 

 depth of the compound zygoma, and the non-articulation of the 

 nasals with the maxillaries on the external surface of the skull, are 

 strictly Ichthyosaurian. 



The posterior position of the nostrils, the small size and position 

 of the palato-pterygoid foramen, are marks of affinity to Plesio- 

 sauruSy in common with which genus the cranial structure of the 

 Ichthyosaurus exhibits a majority of Lacertian characters. 



In comparing the jaws of the Ichthyosaurus tenuirostris with 

 those of the Gangetic Gharrial, an equal degree of strength and of 

 alveolar border for teeth results from two very different proportions 

 in which the maxillary and premaxillary bones are combined toge- 

 ther to form the upper jaw. The prolongation of the snout has 

 evidently no relation to this difference, and we are accordingly led to 

 look for some other explanation of the disproportionate development 

 of the premaxillaries in the Ichthyosaurus : it appears to me to give 

 additional proof of the collective tendency of the affinities of the 

 Ichthyosaurus to the Lacertian type of structure. The backward, 

 or antorbital position of the nostrils, like that in Whales, is related to 

 their marine existence. But, in the Lacertians, in which the nostrils 

 extend to the fore part of the head, their anterior boundaries are 

 formed by the premaxillaries : it appears therefore to be in con- 

 formity with the Lacertian affinities of the Ichthyosaur that the 

 premaxillaries should still enter in the same relations with the nos- 



