THE STRUCTURE OF THE MOTOR ORGANS. 119 



tion (or axis cylinder, see Chap. XII) of a nerve-fibre pene- 

 trates it. 



The striped contents which occupy most of the cavity en- 

 closed by the sarcolemma are the essential contractile portion 

 of the fibre and during life are soft or semi-fluid: soon after 

 death they solidify or clot and thus death-stiffening (rigor 

 mortis] is produced. At intervals, corresponding to the 

 middle zone of each bright band of the relaxed fibre, an 

 extremely delicate membrane (membrane of Krause, K, Fig. 

 58) crosses the fibre, thus dividing the rest of the contents 

 into a series of disks, each consisting of a dim centre answering 



K 



K 



FIG. 58. Diagrams to illustrate the structure of a small piece of a striped 

 muscle-fibre. A, in the relaxed, B, in the contracted condition; K, K, membranes 

 of Krause; H, H, bands of Hensen ; aa, bb, parts of sarcostyles, showing their con- 

 strictions near Krause's membranes, and the tubulated sarcosomes in each ; c,d,e,/, 

 a sarcous element; o, hyaloplasm; g, sarcoplasm. 



to the whole of a dark band, and two brighter ends, each cor- 

 responding to half of a bright band. Each disk is a sar comer e. 

 Under certain conditions, in fact, a fibre may be split up 

 crosswise into a number of such disks. When a fresh muscle- 

 fibre is artificially stretched and examined with a very high 

 magnifying power there may further be made out in the 

 middle of each dim band a transverse line (band of Hensen, 

 H, Fig. 58) slightly brighter than the rest of the dim band. 



The main bulk of each fibre consists of polygonal rods, the 

 muscle-columns or sarcostyles (aa, bb, Fig. 58), which are inter- 



