18 



THE HUMAN MECHANISM 



canal, in which lies the spinal cord 1 the continuation of 

 the central nervous system posterior to the brain. 



FIG. 11 



Model showing the action of muscles on two vertebrae and of the ligaments (I, I') 



in limiting the amount of movement. The contraction of the muscle m stretches 



its antagonist m'. The amount of movement is greatly exaggerated 



Nerves, which pass through small openings in the cranium 

 and between the vertebrae, leave the brain and cord and 

 end in the muscles, skin, glands, 

 and other organs of the body (see 

 Chap. VII). 



12. The appendicular skeleton. 

 The bones of the arm, leg, hand, 

 and foot may readily be felt and 

 are sufficiently familiar. We may, 

 however, call attention to the simi- 

 larity in the number and form of 

 the bones of the arms and legs, a 



similarity which is not only helpful 



FIG. 12. Dorsal view of ver- 



!The terms ft spinal cord," "spinal col- tebrse and ribs 



limn," and "spinal canal" are sometimes showing some of the muscles 

 confused by beginners. The spinal column which lift or raise the ribs 

 is the entire bony framework formed by 



the vertebrae the whole backbone ; it surrounds the spinal canal, which, 

 in turn, contains that part of the nervous system known as the spinal cord. 



