THE CEOCODILIA. 253 



proximal end, between rongli sTitural surfaces furnished by 

 the neural arch above and the centrum below. 



The first caudal vertebra is biconvex, but all the others are 

 procoelous ; those of the anterior moiety of the tail have long 

 ribs fixed in between the neural arches and centra, as in the 

 sacrum, and becoming ankylosed in that position. Chevron 

 bones are attached to the posterior edges of the centra of 

 the vertebrffi, except that of the first, and those of the pos- 

 terior part of tbe tail. 



From seven to nine of the anterior dorsal ribs are united 

 with the sternum by sternal ribs, the form of which varies 

 a good deal in different Crocodilia, being sometimes narrow, 

 sometimes broad and flattened. An elongated plate of 

 cartilage, which may be partially converted into cartilage 

 bone, is attached to the hinder margin of several of the 

 most anterior ribs, above the jimction between the ossified 

 and the cartilaginous part of the vertebral rib. (Fig. 5, Pal) 

 These are the so-called "uncinate processes," which also 

 exist in Hatteria, and reappear in Birds. 



The sternum consists of a rhomboidal plate of cartilage 

 bone, with the posterolateral edges of which two pairs of 

 sternal ribs articulate. The posterior angle of the plate is 

 continued into a median prolongation, which, at length, 

 divides into two curved divergent cornua. From five to 

 seven pairs of sternal ribs are united with the prolongation 

 and its cornua. A long and slender interclavicle lies in a 

 groove of the middle of the ventral face of the rhomboidal 

 part of the sternum. 



In the ventral wall of the abdomen, superficial to the 

 recti muscles, lie seven transverse series of membrane bones, 

 which are termed " abdominal ribs ;" though it must be 

 recollected that they are quite distinct from true ribs, and 

 rather correspond with the dermal ossicles of the Lahyrin- 

 thodonta. Each series is composed of four elongated and 

 more or less cui-ved ossicles, pointed at each end, and so 

 disposed that inner ends of the inner pair meet at an 

 ano-le, open backwards in the middle line, while their outer 

 ends overlap the inner ends of the outer pair. The most 



