i o Physiology. 



Atlas and Axis. The first vertebra, the atlas, has no 

 body. The second vertebra is the axis. It has a peg 

 which runs up into the atlas. In shaking the head, the 

 atlas, with the head, turns on this peg of the axis. In 

 nodding the head, the head simply rocks back and forth 

 on the atlas. 



The Thoracic Vertebras. The twelve rib-supporting 

 vertebras are the thoracic vertebras. 



The Lumbar Vertebras. The next five are the lumbar. 



The Sacrum and Coccyx. The sacrum is composed of 

 five vertebras grown together, and the remaining four are 

 combined in the coccyx. 



Review of the Spinal Column. Let the eye slowly re- 

 view the whole spinal column, noting in what points the 

 vertebras are all alike. Note also their differences. 



Flexibility of the Spinal Column. In well-prepared 

 skeletons there are pads of felt which take the place of the 

 layers of cartilage that were between the vertebras. These 

 cartilages are tough and elastic, and firmly attached to the 

 vertebras above and below. They serve both to keep the 

 vertebras apart and to hold them together. When we bend 

 the shoulders to the right, the right edges of these carti- 

 lages are compressed, and the left edges are stretched, as 

 a piece of india rubber would be if it were glued be- 

 tween the ends of two spools, and the whole were slightly 

 bent. The cartilages also, by their elasticity, protect 

 the brain from the shock it would receive in jumping, 

 walking, etc. 



Curves of the Spinal Column. Vie*w the spinal column 

 from the side. Draw a line representing all its curves. 



