THE MUSCULAR SYSTEM. 



and extremities, they arc invariably thicker (001 G — - 03'") 

 than on the head, in which situation, especially in the facial 



Fig. 90. Fig. 91. 



muscles, they are distinguished by the smallness of their 

 fibres (0005 — 0-01 6'") ; but with respect to this, it is to be 

 remarked that great differences not unfrequently exist in one 

 and the same muscle. From all that is known, it would appear 

 that there is no absolute difference in the size of the muscular 

 fibre in man aud in woman, or between weak and robust 

 individuals. On the other hand, it is not improbable that 

 in one case, one extreme, and in a second the other, may 

 prevail. The thickness of the primitive fibrils, in man, amounts 

 on the average to 00005'"; their number, in one of the larger 

 fasciculi, must reach several hundreds, but is not accurately 

 known. The distance between the transverse striae varies 

 usually from 00004-"' to 0001'". 



[Various controversial opinions still prevail, with respect to 

 the constitution of the muscular fibres. Several authors as- 

 sert, or at all events consider it probable, that the primitive 

 fibrils are produced artificially. This is the opinion entertained 

 by Remak, who thinks a pre-existing division of the muscular 

 cylinder still problematical ; of Briicke, who appears to re- 

 gard the contents of the muscle-tubes during life as fluid j 



Fig. 90. Transverse section of some muscular fibres or primitive fasciculi from 

 the gastrocnemius of man, x 300 diam.: a, sarcolemma and interstitial connective 

 tissue; h, transverse section of t lit- muscular fibrils, with the interstitial substance. 



Fig. 91. Portion of a muscular fibre of man, treated with acetic acid, x 450 diam. : 

 a, sarcolemma ; l>. simple nucleus ; <:. double nucleus, surrounded with fatty molecules. 



