318 THE MECHANICAL TUNCTIONS. 



A farther approach to the higher classes, is observable in 

 the number of cervical vertebrae, which is almost constantly 

 seven; as we shall find it to be in the mammalia. The arti- 

 culations of the vertebrae are similar to those of serpents, in- 

 asmuch as they consist of ball and socket joints. In that of 

 the occipital bone with the first vertebra of the neck, we find 

 that nature again reverts to the simpler form of a single con- 

 dyle projecting from the body of the occipital bone, instead 

 of lateral condyles proceeding from its leaves, as we noticed 

 was the structure in the batrachia. The caudal vertebrae are 

 always numerous, and the tail is compressed vertically, 

 which is the form most favourable for progression in water. 

 They are remarkable, also, for having inferior spinous pro- 

 cesses attached to the bodies by cartilages; a structure ana- 

 logous to that which we have seen in fishes. 



The number of ribs differs in different species of Sauria: 

 they are always articulated to the extremities of the trans- 

 verse processes of the vertebrae, of which they appear to be 

 continuations. Processes of this description also occur in 

 the neck, attached to the transverse processes of the cervical 

 vertebrae; and these have been regarded as cervical ribs. 

 Their presence are impediments to the flexions of the neck; 

 whence arises the difficulty which the crocodile appears to 

 have in bending the neck, while turning round upon the ani- 

 mal he is pursuing. In the thorax, the ribs are connected 

 with a broad sternum; but there are other ribs, both before 

 and behind, which have no such termination, and therefore 

 bear the name oi false ribs. 



The pelvis consists chiefly of the iliac bones, which, as 

 in the batrachia, pass backwards to form the articular cavity 

 for the thigh bone. Two small and slender bones extend 

 forwards from the pubic bones, on the under side of the 

 body, apparently for the purpose of supporting the abdomi- 

 nal viscera.* The bones of the extremities are very perfectly 

 formed, approaching in their shape and arrangement very 



* They appear to be analogous to the marsupial bones peculiar to a family 

 of mammalia. 



