34 



THE HUMAN MECHANISM 



are the muscle fibers. They are 1 to 1J inches in length and 



FIG. 24. Tendon 

 (highly magnified) 



Showing the fiber 

 bundles separated 



from TrrW to ^l"^ of an inch in thickness, thus being from 

 250 to 2500 times . as long as wide, and 

 comparable in shape to a long leather shoe- 

 string rather than to a sausage. Each fascic- 

 ulus contains hundreds or even thousands 

 of fibers. The fibers always run lengthwise 

 of the fasciculus, but, as a usual thing, do 

 not extend its entire length, as obviously 

 follows from the fact that a single fasciculus 

 of the biceps is several inches in length. 

 The fibers are inclosed in a very thin trans- 

 parent membrane, the sarcolemma, and are 

 bound into bundles (or fasciculi) by the 

 same fine connective tissues seen between 

 the alveoli of a gland. To the end of 

 the sarcolemma are attached fine fibers of 

 connective tissue which pass into the tendon 

 (Fig. 25). Indeed, the fibers of the tendon are 

 the collected fibers from the sarcolemmas of all 

 the muscle fibers. For this reason the part 

 of the muscle near the tendon is " tough meat," 

 while that in the belly of the muscle is tender, 

 owing to the smaller number of connective- 

 tissue fibers. 



7. The muscle fiber a cell. The muscle fiber 

 at first sight does not seem like the typical cell 

 already described, with nucleus and cytoplasm ; 

 for when examined in the fresh condition the 

 only obvious points of structure seen in it are showing the at- 

 striking cross striations consisting of alternate tachment of the 

 dark and light bands. It has been shown, how- t g sarco^mnm 

 ever, by ingenious and careful study that the 

 cross striations are optical appearances produced by the 

 peculiar shape of extremely minute longitudinal rods in tho 



FIG. 25. One 

 end of a mus- 

 cle fiber 



