MUSCULAR TISSUE. 99 



ment is occupied by a dark portion, while at each 

 end is a lighter zone. The light and dark zones of 

 the sarcous elements, when the latter are grouped 

 together, form the alternating light and dark bands 

 of the fibres. It is believed by many observers 

 that the sarcous elements are definite and independ- 

 ent structures, in which the dark portion is the 

 contractile element, and that they are joined to- 

 gether side by side and end to end by peculiar 

 cementing substances. 



In addition to these markings on the fibres, if 

 high magnifying powers are used and the fibre is in 

 a state of extension, a fine line is seen crossing the 

 fibre through the centre of the light transverse 

 band ; this corresponds with the dividing line 

 between the ends of the sarcous elements, and is 

 called Krause s line. Under favorable conditions 

 the dark band is also seen to be crossed by a line 

 called Henseris line, whose nature is as yet but 

 imperfectly understood. 



All of the above-described structural features of 

 the muscular fibres are much more distinct after 

 treatment with chemical agents, and after the death 

 of the tissue ; the longitudinal striation is not visible 

 during life, and the distinct separation of the primi- 

 tive fibrillae and discs can only be accomplished by 

 chemical means. We can see the various markings 

 with sufficient clearness, on the fresh or living muscle, 

 to convince ourselves that marked optical differences, 



