10 



Movement— Muscles 



Partnerships of the Muscular System. The business of muscles is to pull; 

 they cannot push. Voluntary muscles in the arms and legs pull from attach- 

 ments to the skeleton; others such as most involuntary ones pull from fibrous 

 attachments. They are specialists in contraction. Skeletons are the frameworks 

 for the hundreds of bodily movements that we see in rabbits or butterflies, 

 bird or man. The nervous system regulates and controls movement that the 

 muscles accomplish with the skeleton as their essential tool (Fig. 10.1). The 

 human brain is helpless to express itself without the contraction of muscles of 

 the face, the eyes, hands, stomach; looking cheerful is a muscular exercise, 

 looking cranky is another in which arms, legs, and face take part. Breathing 

 and the circulation of the blood are completely dependent upon muscular 

 action. When the thoracic muscles are paralyzed by poliomyelitis, breathing 

 cannot go on without an iron lung to take the part of their contraction. 



Compared with other tissues of the body, the activity of muscle demands a 

 large amount of food, but it also liberates a great deal of energy and the major 

 part of bodily heat. And heat is an important catalyst in chemical action, 

 contributing greatly to the more rapid metabolism that is characteristic of 

 warm-blooded animals. 



Muscle constitutes a third to one-half the bulk of vertebrate animals as well 

 as a goodly proportion of it in bees, lobsters, and many other invertebrates. 

 Wherever they occur, muscles and skeleton contribute form as well as function 

 to the body, the pillarlike legs of elephants, the supple foreshoulders of all 

 the cat tribe. The greatest theme of sculpture has been the form and relation- 

 ships and the power of muscles in such figures as the sitting greyhound, resting 

 lion, flying Mercury, as well as those of kings, soldiers, and prophets. Actors 

 on any stage turn the meaning of comedy or tragedy by tricks of their muscles. 

 Without muscles television would be indeed a bleak monotony. All this is not 

 to mention the muscular contractions that control the vocal cords whereby 



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