THE MUSCLES. 215 



668. Each muscle is distinguished into three parts, 

 called the origin, venter or swell, and the insertion or 

 termination. 



669. The origin is that part by which the muscle is at- 

 tached at its upper end ; the swell is the thickest or most 

 conspicuous part, and that which makes up the chief bulk 

 of the whole ; the insertion is the smaller, or tendinous 

 part, being that by which it is attached at the end oppo- 

 site to the insertion. 



670. These three parts are shown by Fig. 121, of 

 which a is the origin, b Pig j 2 i. 



the swell, and c the teiir- 

 dinous insertion. The 

 tendons, in which most 

 of the muscles end, are 

 strong, white, glistening 

 cords, known in the feet 

 of animals under the 

 name of sinews. The tendon in which the muscles of 

 the leg terminate, and which is fastened to the bone of the 

 heel, is a good example of this part of the human frame. 

 It is called the tendo Achilles, and is said to have been so 

 named, because as fable reports, Thetis, the mother of 

 Achilles, held him by this part when she dipped him into 

 the river Styx, to make him invulnerable. Hence that 

 famous hero was said to be proof against all weapons, ex- 

 cept in the right heel. 



671. Names of the Muscles. Every part of the hu- 

 man body which we call fleshy, is covered with muscles, 

 some parts having several layers, one over the other. 

 They all have distinct names by which they are discrimi- 

 nated by anatomical writers. Most of these names are 

 derived from those of the parts where they are situated. 

 Thus the muscles of the breast are called the pectoral mus- 

 cles, from pectus, the breast ; and those extending from the 

 shoulder to the elbow, are called the brachial muscles, 

 from brachium, the arm. Some are, however, named from 

 their shapes, as long, broad, or triangular. 



What are the three parts into which a muscle is distinguished ? What 

 are tendons? What are the nanv>s of the muscles generally derived 

 from? 



