638 BRITISH FOSSIL REPTILES. 



peculiar position of the posterior nostrils of Procoelian Crocodiles, opening vertically 

 behind the bony palate, not horizontally upon that plane, could hardly be adjusted to the 

 relatively larger post-palatine apertures, upon a horizontal plane at some distance from 

 the occiput, with the inner nostrils opening at a more advanced position in the mouth, 

 an arrangement which characterises all Amphiccelians. 



No doubt there were sphincteric structures which would exclude water from the 

 glottis in all the aquatic air-breatliing reptiles, but the peculiar and well-developed 

 valvular contrivances to that end in existing Crocodiles are conditions of the relative size 

 and position of the posterior nostrils in them ; and the repetition of that character in the 

 palatonares of all known tertiary Crocodiles justifies an inference as to the concomitant 

 valvular structures of the soft parts in those extinct Procoelian species, and their con- 

 formity with those in existing Crocodiles. Tliese considerations stimulated or augmented 

 the desire to determine the palatal characters of the fossil skulls of those Crocodilia of 

 the newer Mesozoic formations which, in the massive proportions of their jaws, made the 

 nearest approach to the tertiary and modern kinds. Such demonstration of the struc- 

 ture of the bony palate is accordingly given in the specimens of the Purbeck Crocodiles 

 in the British Museum, described at pp. 632, 634, and figured in Plates 40 and 41. 



Although the jaws of Goniopholis crassidens and GoniophoHs simus have proportions 

 adapted to grapple with large and active Mammals, the evidence of any such warm- 

 blooded air-breathers co-existent with those Crocodilia is not yet acquired. And the 

 probability of such co-existence is, in my opinion, very small, from the circumstance of 

 the palatonares being relatively larger and more advanced than in the Crocodiles con- 

 temporary with great Mammals. The palatonares in Goniojiholis open likewise upon a 

 horizontal plane, look directly downward, not obliquely backward, and, moreover, have a 

 different conformation. With this anatomical character, which I am disposed to asso- 

 ciate with a fish diet, are combined in both Goniopholis and Petrosuchus upper temporal 

 apertures larger than the orbits, and Amphiccelian or Amphiplatyan vertebrae. Now 

 all known tertiary and existing Crocodilia combine with small, posterior, pterygoid 

 palatonares, upper temporal apertures less than the orbits, and in some broad-faced 

 kinds, the upper temporal apertures are almost obliterated by the progressive increase of 

 the osseous roof of the temporal vacuities. These vacuities in the recent reptile are 

 occupied by the temporal muscles, and the power of these biting and holding muscles is 

 in the ratio of the extent of their bony origins. 



In the Amphiccelian fish-eating Crocodilia, the upper temporal apertures are larger 

 and usually much larger than the orbits ; and they are, for the most part, associated 

 with slender jaws and with numerous small uniformly-sized teeth. 



With the palatine modifications, which relate to the drowning of air-breathing prey, 

 and with the cranial developments which relate to the grip of such prey, we find, as a 

 rule, in Procoelian Crocodiles, concomitant modifications in the breadth and strength of 

 the jaws, and in the size of the teeth. There is also inequality of size, favouring hold- 



