THE SKELETON OF THE VERTEBRATE HEAD. 135 



disarticulating the skull of the crocodile the pterygoids 

 generally remain attached to the post-sphenoidal centrum, so 

 that the prolonged anterior processes of the former present 

 the appearance of being elongations of the latter, which they 

 in fact are not. 



From the foregoing considerations, and on grounds to be 

 explained in the sequel, when the palatine arch or haemal arch 

 of the pre-sphenoidal sclerotome conies to be examined, I recog- 

 nise in the crocodilian vomer of Cuvier and Owen the proximal 

 or upper element of the pre-sphenoidal haemal arch the same 

 element to which, when existing in certain fishes, Professor 

 Owen applies the sufficiently expressive term ento-pterygoid. 



It will now be observed, that in consequence of the great 

 development of the pterygoids, and of the ento-pterygoids in 

 the crocodilian, the latter, extending forward into the neural 

 space of the ethmoidal sclerotome, roof over the greater part, 

 and provide a septum for nearly the whole of that extent of 

 the nasal fossse, the sides and floors of which are formed by 

 the so-called " palatals" or ethmoidal neurapophyses, and abut 

 against the descending processes of the " pre-frontals" or 

 ethmoido-frontals, without entirely extruding the neurapo- 

 physes from these processes, as in the chelonian. There is 

 another minor difference between these parts in the croco- 

 dilian and chelonian. In the chelonian, as has been already 

 stated, the ento-pterygoids having pushed the ethmoidal neu- 

 rapophyses from their natural connection with the descending 

 processes of the ethmoido-frontals, complete, by means of their 

 ascending divergent processes, the triangular space for the 

 olfactory nerves. In the crocodilian, again, the descending 

 processes of the ethmoido-frontals complete the space for the 

 olfactory nerves, by means of a short process from each of 

 them, which, passing inwards, meets its fellow of the opposite 

 side a little above the junctions of the descending processes 

 themselves with the ento-pterygoids. The space left between 



