98 VERTEBRAE OF THE CROCODILE. 



face of the vertebrae united by ball and socket. Vertebrae 

 of this " amphicoelian" tj^pe (aju^t, both, xoi^-ko^^ concave) 

 existed in the teleosanrus and steneosaurus. In the ich- 

 thyosaurus, the concave surfaces are usually deepened to 

 the extent and in the form shown in those of the fish 

 (Cut 8). Some of the most gigantic of the crocodilia of 

 the secondary strata had one end of the vertebral centrum 

 flattened, and the other (hinder) end concave ; this " pla- 

 tycoelian" tj^pe (rtxarvj, flat, xotxoj, concave) we find in the 

 dorsal and caudal vertebrae of the gigantic cetiosaurus. 



With a few exceptions, all the modern reptiles of the 

 order lacertilia have the same procoelian type of vertebras 

 as the modern crocodilia, and the same structure pre- 

 vailed as far back as the period of the mosasaurus, and 

 in some smaller members of the lacertilian order in the 

 cretaceous and wealden epochs. 



Resuming the special description of the osteology of the 

 modern crocodilia, we find the procoelian type of centrum 

 established in the third cervical, which is shorter but 

 broader than the second; a parapophysis is developed 

 from the side of the centrum, and a diapophysis from the 

 base of the neural arch ; the pleurapophysis is shorter, its 

 fixed extremity is bifid, articulating to the two above- 

 named processes; its free extremity expands, and its ante- 

 rior angle is directed forwards to abut against the inner 

 surface of the extremity of the rib of both the axis and 

 atlas, whilst its posterior prolongation overlaps the rib of 

 the fourth vertebra. The same general characters and 

 imbricated coadaptation of the ribs (Fig. 18), ^j?, charac- 

 terize the succeeding cervical vertebrte to the seventh 

 inclusive, the hypapophysis progressively though slightly 

 increasing^ in size. In the eisrhth cervical the rib becomes 

 elongated and slender; the anterior angle is almost or 



