32 HUMAN BIOLOGY 



times called, is not only the main connecting structure and 

 support of the body, but it forms a channel through which 

 passes the spinal cord. 



Fig. 32 shows a vertebra, or one of the bones that compose the 

 column. The three projecting points or processes are for the attachment 



of ligaments and muscles. The main body 

 of each vertebra is for supporting the 

 weight transmitted by the column above. 

 Just behind this thick body is a half ring 

 (Fig. 32), which with the half rings on 

 the other vertebrae form the channel for 

 the spinal cord. Between the vertebrae 

 are thick pads of gristle, or cartilage, which 

 act as cushions to prevent jars, and by 

 compression allow bending of the spinal 

 column in all directions. 



The Chest (see Fig. 75). The 

 twelve pairs of ribs are attached 



FIG. 32. -SIDE AND UNDER to the spinal column behind, and 

 VIEW OF A VERTEBRA. , 



extend around toward the front of 



the body, somewhat like hoops. The first seven pairs, 

 called true ribs, are attached directly to the flat breastbone, 

 or sternum. Each of the next three pairs, called false ribs, 

 is attached to the pair above it. The last two pairs, 

 called floating ribs, are free in front. 



The Shoulder Girdle. The collar bones (Fig. 28) can be 

 traced from the shoulders until they nearly meet on the 

 breastbone at the top of the chest. The collar bone is 

 shaped like the italic letter// it helps to form the shoulder 

 joint and holds the shoulder blade out from the chest that 

 the motions of the arm may be free. 



The flat, triangular shoulder blade (Fig. 75) can be felt 

 by reaching with the right hand over the left shoulder. It 

 spreads over the ribs like a fan. Its edges can be made 

 out, especially if the shoulder is moved while it is being 



