CHAPTER IV 



MUSCLES AND TENDONS 



Muscles. The bones of the skeleton are moved by the 

 muscles, which form the chief bulk of the limbs and of 

 a considerable portion of the trunk and give to the body 

 its rounded graceful form. Many of them are imme- 

 diately under the skin, so that we can feel them as they 

 work. If, for example, we grasp with our left hand 

 the large muscle which lies between the shoulder and 

 the elbow on the front of the arm, the biceps, and then 

 pull and push against some object, we can trace 

 the muscle from its origin in the shoulder to its in- 

 sertion upon the radius. We can also feel the dif- 

 ference between the soft elastic belly of the muscle 



when relaxed and its 

 hardness when con- 

 tracted. 



Structure. The 

 structure of muscle 

 can be studied in the 

 flesh of animals, espe- 

 cially in cross section 

 as in a steak. The 

 mass of muscle is seen 



FIG. 31. A small hit of muscle composed of 

 five primary fasciculi. A, natural size; B, 

 the same magnified, showing the secondary 

 fasciculi of which the primary are composed. 



to be made up of fairly large sections, an inch or two 

 in diameter, which can be pulled apart easily, since 

 they are held together only by delicate fibres of connec- 

 tive tissue with a certain amount of fat interspersed. 



Muscle fibres. The large muscle sections are made 

 up of smaller divisions, the fasciculi. Under the micro- 



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