CHAP. VLJ THE MUSCLES. 71 



The internal femoral or adductor muscles occupy the internal 

 portion of the thigh: they are all adductors of the thigh. 



The tibialis anticus, the extensors, and the peroneal muscles 

 cover the front and outer side of the leg. The gastrocnemius 

 and the soleus, the flexors, and the tibialis posticus cover the 

 back of the leg. The action of the tibialis anticus and of one 

 of the three peroneal muscles is to flex the ankle, while the 

 action of the tibialis posticus and the other peroneal muscles is 

 to extend the ankle'. The flexors and extensors act on the toes. 



The gastrocnemius and soleus form th'e calf of the leg ; they 

 are inserted into a common tendon, the ten do Achillis, which 

 is the thickest and strongest tendon in the body, and is inserted 

 into the os calcis, or heel bone. The muscles of the calf possess 

 considerable power, and are constantly called into use in stand- 

 ing, walking, dancing, and leaping; hence the large size they 

 usually present. 



The sole of the foot is protected by a fascia, called the plantar 

 fascia, which is very strong, and the densest of all the fibrous 

 membranes. 



Most of the muscles are covered closely by sheets of fibrous 

 connective tissue (fascise), and this deep layer of tissue forms a 

 nearly continuous covering beneath the superficial or subcu- 

 taneous layer of areolar connective tissue, which in a former 

 chapter we saw to be continuous over the whole of the body. 

 Parts of the deep fasciae in the vicinity 

 of the larger joints, as at the wrist and 

 ankle, become blended into tight trans- 

 verse bands which serve to hold the 

 tendons close to the bones, and receive 

 the name of annular ligaments. 



Relation of muscles to nerves. The 

 function of the muscles is to contract 

 so that their two ends are drawn to- 

 gether, and a movement is thus pro- 

 duced which by various systems of 

 levers can be converted into the par- FIG. 62. NERVE ENDING IN 



,. -, c f , i 17 MUSCULAR FIBRE OF A LIZARD. 



ticular form of motion required. *or (Kuhne } T he end-plate, or mo- 

 example, the Contraction of the mUS- torial ending of the axone, is 



cles of the calf draws the heel upward, s 



and in this way causes the whole body to be elevated on the toes. 



