152 



independent depressed plate, the atlas consisting of seven permanently distinct parts or ele- 

 ments in all Crocodilians. The true centrum of the atlas articulates with the whole of the 

 fore part of the centrum and with the hases of the two neurapophyses of the axis, and deve- 

 lopes on each side two transverse processes, to which the bifurcate head of each pleurapo- 

 physis of the axis articulates. The neurapophyses have coalesced above, and develope a ridgt- 

 or spine from the whole of their antero-posterior extent. Two zygapophyses, with the arti- 

 cular surfaces turned upwards, articulate with the neurapophyses of the atlas. The two 

 posterior zygapophyses of the axis look obliquely downwards and outwards : two short hyp- 

 apophyses project from the under part of the body of the axis. 



This and the following specimens, to No. 701 inclusive, 

 were presented by Prof. Owen, F.R.S. 



684. The sixth cervical vertebra of a Gavial (Gavialis gangeticus). 



The confluence of the neurapophyses with each other and the neural spine above, and the 

 non-development of a distinct hypapophysis, reduce the number of permanently separate 

 elements to four, the centrum, neural arch, and pleurapophyses. The latter are principally 

 developed, as in other Crocodilia, in the antero-posterior direction : the head articulates by 

 suture to the parapophysis, the tubercle by a smaller plane surface with the diapophysis, 

 which is here developed from the base of the neurapophysis : the centrum developes a single 

 hypapophysis, which is here an exogenous process, not, as in most Lacertians, an autogenous 

 element. 



685. An anterior dorsal vertebra of the Gavial (Gavialis gangeticus}. 



The centrum is still characterized by the hypapophysis : the pleurapophyses are elongated, 

 slender and curved : the articulation of the head is transferred to a notch upon the largely- 

 developed diapophysis, the tubercle still articulating to the extremity of that process. There 

 is no parapophysis. 



686. A lumbar vertebra of the Gavial (Gavialis gangeticus). 



It is characterized, as in other Crocodilia, by the absence of the hypapophysis, by the 

 anchylosis of the pleurapophyses, and by the detached hsemapophyses. 



687. The two sacral vertebrae of the Gavial (Gavialis gangeticus}. 



These show the continuous sutural attachment of the head of the short and thick pleur- 

 apophyses, one of which is detached from the posterior vertebra. The sutural surface is 

 divided into two parts, the lower one joining a prominent part of the side of the centrum, 

 answering to the parapophysis, and the upper one to an expansion of the base of the neur- 

 apophysis, which represents the diapophysis. The coadapted surfaces of the centrum are 

 flat : the opposite surfaces are concave in each. 



