146 ANATOMY OF VERTEBRATES. 



mouth is interrupted by the large ' ptery go-maxillary ' vacuities, 

 ib. //, bounded externally by the maxillaries and ectopterygoids : 

 at the fore part is the small ( prepalatine ' opening, ib. p. In the 

 Gavials each pterygoid expands at its outer and fore border into a 

 large oval bulla. The palatines and maxillaries are excavated by 

 sinuses communicating with the nasal passages. The form of the 

 maxillo-premaxillary palatine suture helps by its variation to the 

 distinction of species. 1 The anterior expanded parts of the divided 

 vomer appear upon the bony palate in some Alligators. 2 



The otic capsule remains in great part cartilaginous : towards 

 the cranial cavity it is defended by the thin otocranial plates of 

 the alisphenoid, superoccipital and paroccipital, with occasionally a 

 small scale, representing a rudimental petrosal. The eye-capsule 

 is not defended by bony plates, as in Chelonia. The turbinals 

 remain cartilaginous. 



o 



The cranial cavity is miserably small in these huge cold-blooded 

 Carnivora; its main part, shown in section, fig. 94, 2, o, 10, may 

 be filled by a man's thumb in a skull of three feet in length. The 

 proper brain-chamber is, however, continued along the groove 

 beneath the interorbital platform to the second slight expansion 

 between the prefrontals, 14, where the rhinencephalic (olfactory) 

 lobes send forward the true olfactory nerves. 



If the foregoing statement of the grounds for determining the 

 homologies, general and special, of the skull-bones of the Crocodilia 

 may have seemed tedious or unnecessary, I excuse myself by the 

 importance attached to the subject by Cuvier, who, in the last 

 lecture which he delivered, stated : l If we were agreed as to the 

 Crocodile's head, we should be so as to that of other animals ; be- 

 cause the Crocodile is intermediate between mammals, birds, and 

 fishes.' Admitting, with some latitude, the reason, a sense of the 

 importance of a determination of the bones answerable to those 

 previously defined in Chelonia and Fishes, has influenced me in 

 the foregoing description of the skull of the Crocodilia. 



33. Skull of Opliidia.- -The skull in Lacertians and Ophi- 

 dians departs from the vertebral pattern by a greater degree of 

 confluence and a minor extent of neurapophysial ossification, 

 than in Crocodilia : and that of Serpents manifests more strongly 

 the principle of adaptive developement. 



Eustachian canals in Crocodilia. See also the preparations, XLIV., Nos. 706, 727, 728, 

 750, pp. 154164. 



1 Ib. XLIV., p. 1 63, where that characteristic of Crocodilus rhombifer is specified. 



2 Ib. No. 764, p. 166. 



