408 THE MECHANICAL FUNCTIONS. 



is almost constantly seven ; as we shall find it to 

 be in the Mammalia. The articulations of the 

 vertebrae are similar to those of serpents, inasmuch 

 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 condyle, projecting from the body of the 

 occipital bone, instead of lateral condyles pro- 

 ceeding 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 processes attached to 

 the bodies by cartilages; a structure analogous to 

 that which we have seen in fishes. 



The number of ribs differs in difierent species of 

 Sauria : they are always articulated to the extre- 

 mities of the transverse processes of the vertebrae, 

 of which they appear to be continuations. Pro- 

 cesses 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. They present impediments to the flexions of 

 the neck ; whence arises the difficulty which the 

 Crocodile has in bending the neck while turning 

 round upon the animal he is pursuing. In the 

 thorax, the ribs are connected with a broad ster- 

 num ; but there are other ribs, both before and 

 behind, which have no such termination, and there- 

 fore bear the name of false ribs. 



The pelvis consists chiefly of the iliac bones, 

 which, as in the Batrachia, pass backwards to form 

 the articular cavity fortlie thigh bone. Two small 



