630 PEOF. H. G. SEELEY ON THE CEANIAL CHARACTERS OP 



compressed form of the optic lobes, in the cerebrum tapering ante- 

 riorly, and in the development of bony processes corresponding 

 to the divisions between the chief elements of the brain. The 

 existence of these processes may perhaps be taken as indicating 

 that the brain filled the cerebral cavity ; and therefore these animals 

 present no analogy to Chelonians, which have the brain sheathed 

 in cartilage. This condition of the cerebral region makes a marked 

 difference from Plesiosaurs on the one hand and existing Crocodilia 

 on the other, and supports the idea that the Teleosauria constitute 

 a reptile type in which the obvious resemblances to the living 

 Crocodiles have been somewhat too emphatically insisted upon. It 

 is instructive to compare this section with that of a skull of Igua- 

 nodon figured by Mr. Hulke, where the posterior region, presumably 

 occupied by the cerebellum, is similarly depressed, and anterior to 

 this the brain rises into a convexity for the posterior part of the 

 cerebrum and optic lobes, only without any trace of a bony division 

 between these two regions, such as is seen in this Teleosaur ; and 

 then the brain becomes depressed anteriorly much after the Teleo- 

 saurian pattern, only the cerebrum is relatively short in the Dino- 

 saur, and the brain has its chief extension posterior to the pituitary 

 fossa, which is the reverse of what obtains in the Teleosaurian. 



The Gavial of Caen, named by Geofiroy Teleosaurus cadomensis, has 

 been well figured by Cuvier in the seventh plate of the ' Ossemens 

 Possiles.' His fig. 1 represents a longitudinal section of the skull, 

 which displays a side view of the cast of the cerebral cavity. The 

 total length of the cerebral cavity is 6 centimetres. The specimen 

 shows the cerebrum to consist of a posterior part with an ovate in- 

 flation and smooth lateral surface, which is 2 centimetres long ; but 

 it contracts and becomes depressed anteriorly, and extends forward 

 for about another centimetre. This anterior portion of the brain, 

 something like the olfactory lobes of a mammal or fish, extends 

 under the frontal bone and in advance of its transverse expansions 

 which form the front border of the large temporal fossae. Posterior 

 to the cerebrum the optic lobes are well defined ; they are less wide 

 than the cerebrum, with the sides flattened and depressed in the 

 middle. The cerebellum is rather narrower than the optic lobes, and 

 was evidently less high, with its lateral aspect more rounded. It is 

 thus seen that the anterior part of the brain only occupies about half 

 its length ; and it is difficult to suppose that this length would be 

 greatly augmented were the section made in the middle line of the 

 skull. The optic lobes are far longer than in the Whitby fossil, 

 indicating, I think, a different genus. There are indications of a 

 bony ridge separating the optic lobes from the cerebellum, but no 

 evidence that it descended between these parts of the brain like 

 the otic bones in the specimen described. 



It is impossible to state accurately the depth of bone which 

 covers the brain in the Whitby fossil, because, as already mentioned, 

 the median crest is partly broken away ; but, as preserved, the depth 

 at the posterior termination of the cerebrum is about 2^ centimetres, 

 while the thickness of the bone at the anterior termination is about 



