456 



MOTION. 



in both instances a bad one, it certainly is an unsatisfactory 

 one, but it is as good for one case as the other. 



MUSCULAR MOTION. 



There are two chief kinds of muscular tissue, the striped, 

 and the plain or unstriped, and they are distinguished by struc- 

 tural peculiarities and mode of action. The striped form of 

 muscular fibre is sometimes called voluntary muscle, because 

 all muscles under the control of the will are constructed of it. 

 The plain or unstriped variety is often termed involuntary, be- 

 cause it alone is found in the greater number of the muscles 

 over which the will has no power. 



The involuntary or unstriped muscles are made up, accord- 

 ing to Kolliker, of elongated, spindle-shaped, nucleated fibre- 

 cells (Fig. 155), which in their most perfect form are flat, from 

 about ^^ to -3-3^0 of an inch broad, and about g ^ to 8 -Jn of 

 an inch in length very clear, granular, and brittle, so that 



FIG. 155. 



FIG. 156. 



FIG. 155. Muscular fibre-cells from human arteries, magnified 350 diameters 

 (Kolliker). a, natural state; b, treated with acetic acid. 



FIG. 156. Plain muscular fibres from the human bladder, magnified 250 diameters, 

 a, in their natural state ; 6, treated with acetic acid to show the nuclei. 



when they break, they often have abruptly rounded or square 

 extremities. Each fibre-cell possesses an elongated nucleus, 

 and many are marked along the middle, or, more rarely, along 



