THE STRUCTUBE OF THE ELEMENTARY TISSUES. 85 



may be seen to be divided in 1 the middle line by other very fine trans- 

 verse dark lines, sometimes called Dobie's line. 



(c.) Each dark stripe may also sometimes be seen to be divided by a 

 clear line, called Benson's disc. 



(d.) Each fibre presents an appearance of longitudinal striation and 

 after ^hardening in alcohol may be divided by teasing with needles into 

 longitudinal fibrils, more or less cylindrical or angular, which are named 

 muscle columns or sarcostyles, and extend throughout each fibre. Each 

 of these appears to consist of short columns connected together by 

 bright intervals, the former are the sarcous elements of Bowman. They 

 may possibly be further longitudinally striated, and so made up of finer 

 fibrill^e still. 



After treatment with reagents the fibre may be split up into trans- 

 verse discs. 



(e.) On Transverse Section. The fibre presents most externally, 

 the outline of the sarcolemma. 



(f.) The muscular substance proper appears to be mapped out into 



Fig. 87. Three muscular fibres running longitudinally, and two bundles of fibres in transverse sec- 

 tion, M, from the tongue. The capillaries, C, are injected. X 150. (Klein and Noble Smith, j) 



small polygonal areas by clear lines (fig. 83) called Colmheim's fields, the 

 lines giving the appearance of a mesh work. The lines represent the 

 transverse section of the cementing material between the sarcostyles, 

 which is called sarcoplasm. 



(g.) Immediately within the sarcolemma in ordinary muscle or in 

 the centre of the fibre as in the muscle of some insects, are seen clear 

 oval nuclei called muscle nuclei or muscle corpuscle, surrounding which 

 is a certain amount of granular protoplasm (fig. 85). 



The appearances of the muscle fibre when seen under the micro- 

 scope, cannot be said to be yet thoroughly understood, and have given 

 rise to various theories as to the structure of striped muscle, to several 

 of which it will be as well to allude. 



Muscle Caskets (Krause) Theory. According to this view a 

 muscle fibre is made up of transverse compartments, bounded laterally 

 by the sarcolemma, and above and below by a fine membrane, called 



