40 PHYSIOLOGY AND TEMPERANCE. 



muscle is drawn up into a large solid lump at its middle. 

 Now, if_onejjen^_j8-Amly_a.ttached to a bone, its origin, and 

 the other to a strong tendon which passes down to "the bone 

 below, its, in^^rfaon. the lower bone will necessarily be drawn 



towards the upper. This 

 may be understood by 

 bending the elbow with 

 the arm bare. As the 

 body of the biceps mus- 

 cle swells out and be- 

 comes hard and firm, 

 the forearm is drawn 

 up. When the nerve 

 influence is withdrawn, 



the muscle relaxes and 

 Fio. 17.-Biceps and Triceps Muscles. 



3. Arrangement of Muscles. The muscles are usually 

 arranged in groups, and these have opposing groups on the 

 opposite side of the limb. Take, for example, the leg. One 

 set of muscles bends the knee, so that the leg is flexed upon 

 the thigh. These are called flexors. Another set brings the 

 leg forward, and extends it out until it is in a line with the 

 thigh. These are. called extensors. It is by this nice adjust- 

 ment of opposing systems of muscles throughout the body 

 that we are able to stand erect and to move about with ease 

 and comfort. 



This even action of the many pairs of muscles all over the 

 body also maintains its symmetry. If one muscle or group of 

 muscles acts more strongly than the opposite, the limb is 

 twisted. This is the case in the deformity known as club- 

 foot. The foot may be drawn outward by the muscles on the 

 outside of the leg acting more strongly than those on the 

 inside, or it may be drawn inward if the inner muscles are 

 stronger than the outer. In the same way the spine mav 



