160 STUDIES IN PHYSIOLOGY 



anism of the inner ear is hidden within the hardest bone of 

 the body ; and the organs of the chest cavity are well pro- 

 tected by the ribs and breastbone. 



In other parts of the body, as in the arms and legs, the 

 skeleton is surrounded by the muscles, nerves, and other 

 tissues. Here the bones act as levers, which are moved by 

 the muscles whenever we wish to go from place to place, or 

 whenever we desire to move things about us. 



In a word, then, the bony framework (1) gives to the body 

 its permanent shape, (2) protects delicate organs, (3) pro- 

 vides a leverage on which muscles may act. 



Regions of the Skeleton. For convenience, the two hun- 

 dred bones of the skeleton may be divided into three groups, 

 namely, (1) the bones of the arms and legs, (2) the bones of 

 the neck and trunk, and (3) the bones of the head (Fig. 63). 



1. THE SKELETON OF THE AKMS AND LEGS 



Bones of the Arm. The skeleton of the upper arm (see 

 Fig. 64, B) is formed by a single long bone called the hu'me- 

 ruSj which extends from the shoulder to the elbow. In the 

 forearm, one can feel through the flesh two separate long 

 bones, of about the same size, lying side by side ; the bone 

 on the thumb side of the forearm is the ra'di-us ; on the little 

 finger side is the ul'na. Two rows of small bones, more or 

 less cubical in shape, are found in the wrist. These eight 

 wrist or car'pal bones move freely upon each other, and thus 

 give the hand a great range of movement. By pressing with 

 the finger on the back of the hand, one can distinguish five 

 rather long bones, and since these lie beyond or distal to 

 the carpals they are called met-a-car'pal bones (Greek meta= 

 beyond + karpds = wrist). The skeleton of each finger is 

 formed of three separate bones, and in the thumb there are 

 two bones. These fourteen bones of the digits are called 

 pha-lan'ges (because of the arrangement of bones in succes- 

 sive rows like the soldiers in the Greek phalanx). 



