SKELETON OF THE HATRACHIA. 393 



Tlie skeleton of the adult frog is shown in Fig. 

 200 ; from which it will be seen that the spinal 



column is comparatively much shorter than that of 

 fishes, or indeed of any other class of animals; for 

 it consists of only eight vertebrae, exclusive of those 

 which have united to form the os coccygis. It was 

 evidently the intention of nature to consolidate the 

 framework of the trunk, in which flexibility was 

 not required for progressive motion ; the perform- 

 ance of that function being transferred to the hind 

 extremities, which are exceedingly large in pro- 

 portion to the rest of the body. There is a tendency 

 in every part of the skeleton to develope itself in a 

 transverse direction, while the trunk is shortened 

 as much as possible. 



The mode in which the vertebrae are articulated 

 together differs widely from what we have seen in 

 fishes, and approaches to the structure of the higher 

 classes of vertebrata. The body of each vertebra, 

 instead of having at its posterior surface a cup-like 

 cavity, terminates by a projecting ball, which is 



