OSSEOUS SYSTEM. 141 



corresponds to the manubrium, and behind this of a very broad, 

 flat, cartilaginous piece representing the body of the sternum, 

 whereunto are appended posteriorly two small elongated pieces, 

 parallel with each other, which, but for their receiving some of the 

 costal cartilages, might be regarded as analogous to the ensiform 

 cartilage of the Mammalia. The sternum becomes smaller, and 

 more rudimentary in Chirotes, where the ensiform cartilage is 

 formed by the uni-perforate plate of the body of the bone. In An- 

 guis, even this is wanting, and there is only left a thin cartilaginous 

 plate behind the clavicles ; while in Pseudopus, the T-shaped manu- 

 brium is present along with it, though furnished with shorter pro- 

 cesses. 



The Crocodiles exhibit in the conditions of their skeleton, as in 

 other general points of structure, various departures from the type 

 of the remaining Sauria. The relative number of the vertebrae, 

 with the exception of the caudal, agrees with that of the human 

 subject, there being seven cervical, twelve dorsal, and five lumbar. 

 The atlas is remarkable for consisting of four pieces, and support- 

 ing, as does also the second cervical vertebra, a moveable bone or 

 rib of considerable size. The five succeeding vertebrae of the neck, 

 like the twelve dorsal vertebrae, have their laminae united by 

 suture to the vertebral bodies, and support also short rib-like ap- 

 pendages, which are attached, like true ribs, by two crura, or in a 

 furcate manner to the double (superior and inferior) transverse 

 processes, and terminate externally by a hammer-shaped head, the 

 anterior and posterior ends of which lie in such a way upon those 

 of the adjoining vertebrae, as to limit the movements of the vertebrae 

 in the lateral direction. This structure explains the fact, why one 

 can easily escape when pursued, from a Crocodile, by moving in a 

 circle. The sternum is broad anteriorly, and there projects into a 

 pointed and free median process, while posteriorly it extends by 

 means of two long slender pieces (sternal ribs), as far as the pubis. 

 The part opposite to the lumbar vertebrae supports five pairs of free 

 costal cartilages, without any vertebral ribs. There are only two 

 sacral vertebrae, as in the rest of the Sauria, and about forty caudal 

 vertebrae. 



It is in the Chelonia unquestionably that the vertebrae, ribs, and 

 sternum, present the most abnormal structure, for it is in them that 

 a coalescence of some of the tegumentary bones takes place with 

 those of the true skeleton, so as to form the dorsal shield, or cara- 

 pace, and the ventral or plastron. The cervical vertebras, eight in 



