ANATOMY OF VERTEBRATES. 65 



but they are more ossified, and the hyo- and hypo-stemals unite 

 suturally with the fourth, fifth, and sixth marginal plates, forming 

 the side-walls of the bony chamber cut through in fig. 51. The 

 junction between the hyo- and hypo-sternals admits of some 

 yielding movement. The iliac bones abut against the pleurapo- 

 physes of the tenth, eleventh, and twelfth vertebra?, counting from 

 the first dorsal vertebra. These three vertebras form the sacrum : 

 their pleurapophyses are unanchylosed, converge, and unite at 

 their distal extremities to form the articular surface for the ilium. 

 Beyond these the caudal vertebra?, ib. h, thirty-five in number in 

 Testudo elephantopus, are free, with short, straight, and thick 

 pleurapophyses, articulated to the sides of the anterior expanded 

 portions of the centrums. They diminish to mere tubercles in the 

 tenth caudal vertebra, and disappear in the remainder. The neural 

 arches of the caudal vertebra? are flat above, and without spines. 



§ 24. Vertebral column of Crocodilia. — In this order free 

 pleurapophyses are developed from all the cervical vertebra? ; that 

 of the atlas, fig. 54, a, is attached to the hypapophysis ; the neur- 

 apophyses rest, in part upon this element, in part upon the proper 

 centrum, which coalesces with that of the axis : the neural spine 

 of the atlas remains distinct, like that of the occiput, and is broad 

 and flat. The centrum of the axis is flat in front, and convex 

 behind : the neural arch, as in the succeeding vertebra, is com- 

 pleted by the connate spine. The pleurapophysis, ib. b, has a 

 bifurcate head. With the exception of the two sacral vertebra?, 

 which are flat at one end and concave at the other, and of the first 

 caudal vertebra, which is convex at both ends, the bodies of 

 all the vertebra? beyond the axis are concave in front and convex 

 behind. The procoelian centrum of the third cervical 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 anterior angle is directed forward 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 imbri- 

 cated coadaptation of the ribs, not given in the diagram, 54, 

 characterize the succeeding cervical vertebra? to the seventh 

 inclusive, fig. 57, p, the hypapophysis progressively though slightly 

 increasing in size. In the eighth cervical the rib, h, becomes 

 elongated and slender ; the anterior angle is almost or quite 

 suppressed, and the posterior one more developed and produced 



VOL. I. F 



