SKELETONS OF BIRD AND REPTILE 



23 



latter is a ball-and-socket. At the hinder end of eacli 

 vertebra there is a protuberance, rounded on its upper 

 side but nearly flat below, which fits into a hollow in 

 the vertebra behind. The fact that the protuberance is 



Fig. 7.— (A) Two vertebrae of Snake. (/?) Two neck vertebr.x of Eagle. 



I. Anterior end. II. Posterior. 



b, ball ; cr, cervical rib; sd. "saddle" ; sk, socket ; sf, spine ; va, tunnel through 



which vertebral artery passes. 



not a perfect ball but has its underside flattened limits 

 the freedom of movement, and, in addition to this, each 

 vertebra bears a spine (SP, fig. 1 ) upon the top, the spine 

 of one being very near to that of the next, and thus 

 a further limit is put to movement up and down. The 



