BONES, MUSCLES, EXERCISE, AND REST. 261 



The muscles form the most abundant part of the body. 

 They constitute the great b.ulk of the limbs, the back, and 

 neck. They cover the face and chest, and form the principal 

 portion of the walls of the abdomen. In lower animals, they 

 are the lean meat which we eat upon our tables. They con- 

 sist of stringy fibres, that usually lie parallel with each other, 

 and are fastened, by a strong whitish-looking substance, into 

 bundles. Each bundle, thus fastened together, forms one 

 muscle. 



616. These muscular fibres have* a power of drawing up or 

 contracting, like the earth worm ; and when they thus con- 

 tract, they draw their ends toward each other, and draw to- 

 gether or move toward each other whatever parts or bones 

 may be fastened to these ends. 



617. All the parts of the body that move are furbished with 

 some ofthes&jmiscjlcs, or bundles of lean flesh. There are five 

 hundred and twenty-seven muscles in the human body. Five 

 hundred and fourteen of these are in pairs, being the same on 

 the two sides, and thirteen others are single muscles, as the 

 heart, &,c. These are arranged in layers, and in some parts 

 of the body, as on the back and the large limbs, there are 

 several layers between the skin and the bones. Some of the 

 outer layers are shown in Figures XLIX., L., and LI. The 

 inner layers are shown in Figures LII., LIV., LV., and. LVII. 



618. The cutaneous rpuscle, (Fig. XLIX. ,) is attached to 

 the skin and flesh, of the cjieek above, and of the neck below. 

 It aids in drawing the mouth downward. 



The deltoid, XLIX. 6, or triangular muscle, has its upper 

 side, or ends of the fibres, attached to the collar-bone and 

 shoulder-blade. These fibres meet in a point, which is at- 

 tached to the humerus or bone of the upper arm. Its front 

 fibres draw the arm upward and forward ; its back fibres draw 

 the arm upward and backward ; and all, together, lift the arm. 



The biceps, or two-headed muscle of the arm, XLIX. c. and 

 LI. b, is attached above to the shoulder-blade and the upper 

 part of the humerus, and sends a cord to the lower arm near 

 the elbow. It bends the elbow. 



