VERTEBRAE OF THE CROCODILE. 97 



in tlie cervical series wliicli does not support a- rib ; it 

 articulates by suture with its neurapopliyses nx^ and is 

 cbaracterized by having its anterior surface flat, and its 

 posterior one convex. 



With the exception of the two sacral vertebrae, the 

 bodies of which have one articular surface flat and the 

 other concave, and of the first caudal vertebra, the body 

 of which has both articular surfaces convex, the bodies of 

 all the vertebrae beyond the axis have the anterior articular 

 surface concave, and the posterior one convex, and arti- 

 culate with one another by ball-and-socket joints. This 

 type of vertebra, which I have termed "procoelian" (rtpoj, 

 before, xoitloj, concave), characterizes all the existing genera 

 and species of the order Orocodilia with all the extinct 

 species of the tertiary periods, and also two extinct species 

 of the greensand formation in New Jersey.^ Here, so 

 far as our present knowledge extends, the type was lost, 

 and other dispositions of the articular surfaces of the 

 centrum occur in the vertebra of the crocodilia of the 

 older secondary formations. The only known crocodilian 

 genus of the periods antecedent to the chalk and green- 

 sand deposits with vertebrae articulated together by ball- 

 and-socket joints, have the position of the cup and the 

 ball the reverse of that in the modern crocodiles ; and one 

 genus, thus characterized by vertebrae of the "opistho- 

 coelian" type (ortta^oj, behind, xoao?, concave), has accord- 

 ingly been termed streptospondylus, signifying " vertebrae 

 reversed." But the most prevalent type of vertebra 

 amongst the crocodilia of the secondary periods was that 

 in which both articular surfaces of the centrum were con- 

 cave, but in a less degree than in the single concave sur- 



' "Quarterly Journal of the Geological Society," November, 1849. 

 9 



