54 



ANATOMY FOK NURSES. 



[CHAP. VI. 



R 



substance ; this, however, is not proved, and the ultimate struct- 

 ure of muscular fibre is still by no means fully understood. This 

 much, however, is certain, that the contractile substance is a com- 

 plex chemical structure, and that the molecules of which it 

 is composed readily change their places under the influence of 

 certain stimuli. When a muscle contracts, each section or 

 sarcous element of the fibre broadens and shortens. This 

 broadening and shortening is brought about by the molecules 



of each section of the fibre 

 changing their places. We 

 shall have a rough image of the 

 movements of the molecules 

 during a muscular con traction 

 if we imagine a company of 

 a hundred soldiers ten ranks 

 deep, with ten men in each 

 rank, rapidly, but by a series 

 of gradations, extending lat- 

 erally into a double line 

 with fifty men in each 

 line. 



The striated muscles are 

 all connected with nerves, 

 and under normal conditions 

 do not contract otherwise 

 than by the agency of the 

 nerves. They are also plenti- 

 fully supplied with blood- 

 vessels. 



The muscular fibres lie 

 closely packed, their ends 

 lapping over on to adjacent 



FIG. 53. -WAVE OF CONTRACTION PASS- fibres, and forming bundles. 

 ING OVER A MUSCULAR FIBRE OF DYTLSCUS. 

 Very highly ma-nified. if, K, portions of Ihese bundles are grouped 



** 







. 



and in this way the muscles 

 which are attached to the skeleton are formed. 



Involuntary, non-striated muscular tissue is composed of long, 

 somewhat flattened, elongated fibre-cells. Each fibre-cell con- 

 tains an oval or rod-shaped nucleus, containing one or more 



