Page:Quarterly Journal of the Geological Society of London, vol. 34.djvu/507

Rh OP A HTGHEE POEM OP LIFE Otf A LOWEE POEM. 425

ference as to the concomitant valvular structures of the soft parts in those extinct proccelian species.

These considerations stimulated or augmented the desire to deter- mine the palatal character 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 structure of the bony palate is accordingly given in the specimens of the Purbeck Crocodiles in the British Museum, which form the subject of my " Monograph on British Fossil Reptilia," in the volume of the Palaeontographical Society for 1878.

Although the jaws of Goniopholis crassidens and Goniopholis simus have proportions "adapted to grapple with large and active mammals, the evidence of any such warm-blooded air-breathers coexistent with those Crocodilia is not yet acquired. And the probability of such coexistence is, in my opinion, very small, from the circumstance of the palato-nares being relatively larger and more advanced than in the Crocodiles contemporary with such mammals. The palato- nares in Goniopholis open likewise upon a horizontal plane, look directly downward, not obliquely forward, and, moreover, have a different anatomical conformation. Instead of being formed or bounded by the pterygoids exclusively, as in Tertiary Crocodiles, the palatine bones enter into the formation of the anterior third of the circumference of the palato-nares.

With this anatomical character, which I am disposed to associate 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 palato-nares, upper temporal apertures (fig. 2, t) less than the orbits (ibid, o) ; 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 vacui- ties, 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 (fig. 5, t) are larger, and usually much larger, than the orbits (o) ; and they are, for the most part, associated with slender jaws and with numerous, small, uniformly sized teeth (fig. 4).

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 proccelian Crocodiles, concomitant modifications in the breadth (fig. 2) and strength of the jaws, in productions of the alveolar borders, and in the size of the teeth (fig. 1). There is also inequality of size, favouring holdfast, as in mammalian Carnivora ; and certain teeth of the dental series have accordingly received the name of canines in the Crocodiles with such analogous dentition.

In this comparison and its applications I propose at present to Q.J.G.S. No. 134. 2p