SKELETON 



51 



behind the junction there are only two little vertebrae 

 to represent the tail bones. Xote also that the for- 

 ward end of this bonj rod (called the itrostyle) has on 

 each side a projection against which the bones to which 

 the leos are fastened join directly. This really makes 

 three stiff rods side by side in the back here to resist 



Fig. 23. — Skck-tuii oi frug. 



the sudden thrust of the powerful hind legs. Many- 

 creatures leap, but none have themselves hurled for- 

 ward by a stroke directly at the rear end of the spinal 

 column, as the frogs. These projecting pieces at the 

 forward end of the rod are called " the transverse 

 processes of the sacral vertebrae," and may or may 

 not be more or less expanded at their outer ends, 



