CAUSES AND PHENOMENA OF MOTION. 



17 



of Briicke. When seen in transverse section the contractile discs appear 

 to be subdivided by clear lines into polygonal areas, Cohnheim's fields 

 (Fig. 271), each corresponding to one sarcous element prism. The clear 

 lines are due to a transparent interstitial fluid substance pressed out of 

 the sarcous elements when they coagulate. There is still some doubt 

 regarding the nature of the fibrils. Each of them appears to be com- 

 posed 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 pellucid substance continuous with them. 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 



FIG. 267. A. Portion of a medium-sized human muscular fibre. X 800. B. Separated bundles 

 of fibrils equally magnified; a, a, larger, and 6, b, smaller collections; c, still smaller; d, d, the 

 smallest which could be detached, possibly representing a single series of sarcous elements. (Sharpey.) 



sarcous elements is composed of a number of other fibrils still finer, so that 

 the sarcous element of an ultimate fibril would be not quadrangular, but 

 as a streak. 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. 267, B, d). 



A fine streak can usually be discerned passing across the interstitial 

 disc between the sarcous elements: this streak is termed Krause's mem- 

 brane: it is continuous at each end with the sarcolemma investing the 

 muscular fibre (Fig. 266, B). 



Thus the space enclosed by the sarcolemma is divided into a series of 

 compartments by the transverse partitions known as Krause's membranes; 

 these compartments being occupied by the true muscle substance. On 

 VOL. II. 2. 



