Chap. 10 MOVEMENT MUSCLES 159 



tachment is by a tough and very flexible but inelastic tendon (Fig. 10.3). 

 Like many muscles, the biceps and triceps of the arm work in opposition. The 

 biceps muscle contracts and, as the arm bends the triceps is stretched. The 

 triceps contracts; the arm straightens, and the biceps is stretched. 



The great advantage of tendons is in their strength, considering the small 

 space they occupy. The cords on the back of the hand, each attached to a 

 finger bone, are the tendons of muscles that straighten the fingers. All of these 



Myofibrils (l-2>i) 



Nuclei of Muscle Fiber 



Muscle Fiber Crushed 

 1 K' ''^^^iZZ Showing 



MV/Wl/'fa ^'^^' Membrane (l/») 



Connective Tissue Cells 

 (Perimysium) 



Fig. 10.4. A group of skeletal or striated 

 muscle cells commonly called fibers. Some of 

 the fibers are cut oflf to show them in cross 

 section. A skeletal muscle fiber is actually a 

 sort of super-cell containing many nuclei and 

 other cell elements, a highly specialized struc- 

 ture. (Courtesy, Gerard: The Body Functions. 

 New York, John Wiley & Sons, 1941.) 



^jAo.-,. E>-r'o 



muscles are located in the forearm and depend on the tendons to communicate 

 their pull (Fig. 9.16); if the muscles were near the fingers the back of the 

 hand would be a bulging pillow. By a similar arrangement in the leg, the calf 

 muscle (gastrocnemius) lifts the heel by its tendon of Achilles (Fig. 9.16). 

 Picture the tendon of Achilles omitted and the calf muscles moved to their 

 immediate place of business at the heel! 



Conditions of Muscular Activity. Muscles contain an enormous number of 

 blood and lymph capillaries, the former apparently in contact with every mus- 

 cle cell (Fig. 10.7). The glycogen stored in muscle cells is a readily oxidized, 

 quickly available food. An extra amount of blood flows into muscles as soon 



