CROCODILIA. 87 



of vertebra amongst the Crocodilia of the secondary periods was that in which both 

 articular surfaces of the centrum were concave, but in a less degree than in the single 

 concave surface of the vertebrae united by ball and socket. A section of a vertebra 

 of this ' amphicoelian' type, such as existed in the Teleosaurus and Steneoscmrus, is 

 figured in PI. 4, fig. 6. In the Ichtlnjosaurm, the concave surfaces are usually deepened 

 to the extent and in the form shown in fig. 7. 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 ' platycoehan' type we find in the dorsal and caudal 

 vertebrae of the gigantic Cetiosaums (PI. 4, fig. 5). 



With a few exceptions, all the modern Reptiles of the order Lacertilia have the same 

 procoelian type of vertebrae as the modern Crocodilia, and the same structure prevailed 

 as far back as the period of the Mosasaurus, and in some smaller members of the 

 Lacertilian order in the Cretaceous and Weal den 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 ex- 

 tremity expands, and its anterior 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 pro- 

 longation overlaps the rib of the fourth vertebra. 



The same general characters and imbricated coadaptation of the ribs characterise 

 the succeeding cervical vertebrae to the seventh inclusive, the hypapophysis {/i!/, fig. 2, 

 PL 1 B) progressively though slightly increasing in size. In the eighth cervical the 

 rib becomes elongated and slender ; the anterior angle is almost or quite suppressed, 

 and the posterior one more developed and produced more downwards, so as to form 

 the body of the rib, which terminates, however, in a free point. In the ninth 

 cervical the rib is increased in length, but is still what would be termed a 'false' 

 or ' floating rib' in anthropotomy. 



In the succeeding vertebra the pleurapophysis articulates with a haemapophysis, and 

 the haemal arch is completed by a haemal spine ; and by this completion of the typical 

 segment we distinguish the commencement of the series of dorsal vertebrae. With regard 

 to the so-called ' perforation of the transverse process,' this equally exists in the present 

 vertebra, as in the cervicals, as may be seen by comparing fig. 6, p. 5, with fig. 2, PI. 1 D; 

 in both, the foramen is the vacuity intercepted between the bifurcate extremity of the rib 

 and the rest of the vertebra with which that rib articulates ; and, on the other hand, 

 the cervical vertebrae equally show surfaces for the articulation of ribs. Cuvier, in 

 including the proximal portions of the ribs with the rest of the vertebra, in his figure 

 of a dorsal vertebra of a Crocodile, * so far follows nature, and produces a parallel to 



* Ossemens Fossiles, -Ito, torn, v, pt. ii, pi. iv, fig. 4. 



