STRUCTURE OF STRIPED MUSCLE. 459 



filaments or primitive fibrils of which the substance of each 

 fibre is composed (Fig. 160). 



The whole substance of the fibre contained within the sarco- 

 lemma may be thus supposed to be constructed of longitudinal 



FIG. 159. FIG. 160. 



FIG. 159. Muscular fibre torn across ; the sarcolemma still connecting the two 

 parts of the fibre (after Todd and Bowman). 



FIG. 160. A few muscular fibres, being part of a small fasciculus, highly magni- 

 fied, showing the transverse striae, a, end view of b, b, fibres ; c, a fibre split into 

 its fibrils (after Sharpey). 



fibrils a- bundle of fibrils surrounded by the sarcolemma con- 

 stituting a fibre. 



There is still some doubt regarding the nature of the fibrils. 

 Each of them appears to be composed of a single row of minute 

 dark quadrangular particles called sarcous elements, which are 

 separated from each other by a bright space formed of a pel- 

 lucid substance continuous with them. A fine streak can be 

 sometimes discerned passing across the bright interval between 

 the sarcous elements. Dr. Sharpey believes that, even in a 

 fibril so constituted, the ultimate anatomical element of the 

 fibre has not been isolated. He believes that each fibril with 

 quadrangular sarcous elements is composed of a number of 

 other fibrils still finer, so that the sarcous element of an ulti- 

 mate fibril would be not quadrangular but as a streak, and the 

 dark transverse streak on the bright space but a row of dots. 

 In either case the appearance of striation in the whole fibre 

 would be produced by the arrangement, side by side, of the 

 dark and light portions respectively of the fibrils (Fig. 161). 



