'212 FOSSIL REPTILES. 



not altogether a new bone peculiar to the animal, is at least a 

 decided dismemberment from the sphenoid, as the fore and 

 hind frontals which we have mentioned are dismemberments 

 of the frontal bone. It can by no means be compared to any 

 of the bones naturally distinct in the foetus of the mammalia. 

 M. Cuvier has, therefore, bestowed upon it a particular name, 

 calling it the transverse bone. 



In the Crocodile, as in the other ovipara, many parts of the 

 ethmoid remain cartilaginous. Four alone become osseous. 

 The first, or lower two, are articulated to the internal edge of 

 the palatines in front of the anterior frontals, and of the vaulted 

 portion of the ossa pterygoidea. Between them and the 

 neighbouring part of the palatines, commences on each side 

 the double canal of the back nostrils, which proceeds to ter- 

 minate at the posterior edge of the ossa pterygoidea. These 

 pieces are analogous to the lower and canaliculated part of the 

 vomer in quadrupeds. 



The two other ossified pieces of the ethmoid adhere to the 

 roof of the nostrils, between the nasal, the lachrymal, the 

 anterior frontal, and the chief frontal bones. Nothing of them 

 is to be seen externally in the caymans or the gavials. But 

 they are easily distinguishable in part outside, between the 

 frontal and nasal bones in the crocodiles proper. They are 

 manifestly analogous to some portion of the upper cornets. 



We must now speak of the temporal bone, and determine 

 the analogy of its parts. 



In the foetus of mammalia this bone is divided into four 

 pieces: — 1. The squamous and zygomatic, which, as we 

 descend in the scale of quadrupeds, becomes more and more 

 foreign to the cranium, so that in the ruminants it appears 

 rather pasted or glued on above, than entering into the compo- 

 sition of the parietes of the skull. — 2. The tympanic, having 

 at first in the foetus no part ossified, except the frame of the 

 tympanum, and extending itself successively so as to form an 

 OS tympani, and a meatus externus, — 3. The petrous portion 



