THE SKELETON AND THE MUSCLES 



291 



tives of the tarsal bones of the ankles, and these are 

 followed by the metatarsals, and these again by the 

 phalanges which are the skeletal elements of the toes. 

 At the knee there is a small, rounded bone, the patella or 

 knee pan. 



The kind of material that is usually eaten as meat 

 consists mainly of muscle, a tissue whose chief function 

 is the production of movement. We are able to move 

 only because our muscles have the property of shortening 

 or contracting under the influence of stimuli. Grasp 

 the upper arm with one hand while 

 you bend the fore arm, and you 

 can feel the large muscle in front 

 of the humerus (the biceps) shorten 

 and thicken. When you straight- 

 en the arm you can feel an op- 

 posed muscle (triceps) contract on 

 the opposite side. In moving the 

 arm the bones act as levers which 

 are pulled this way and that by 

 the muscles attached to them. 

 Muscles never act by pushing, the 

 opposed movement being always 

 effected by the contraction of an 

 antagonistic muscle. Accordingly 



we commonly find muscles in pairs the members of which 

 have opposed functions. If a part is pulled in any one di- 

 rection there must be some other muscle to pull it back 

 again. Muscles are usually attached to bones, sometimes 

 directly and sometimes by means of strong inelastic cords, 

 or tendons. You can easily feel the tendons of your biceps 

 muscle or the tendons of some of the muscles behind the 

 knee or at the wrist. 



The contractile tissue is made up of fibers, which are 



FIG. 209. Diagram 

 showing the action of the 

 biceps muscle b, which when 

 it contracts moves the fore 

 arm in the direction of the 

 arrow. 



