CILIAET A:NT> MITSCULAE MOTION. 



581 



because all muscles under the control of the will are con- 

 structed of it. The plain or unstriped variety is often 

 termed involuntary, because 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, 

 according to Kolliker, of elongated, spindle-shaped, nu- 

 cleated fibre-cells (fig. 155), which in their most perfect 

 form are flat, from about -4^77 ^ 3~r<ro ^ an * ncn broad, 

 and about -gJ-g. to T ~- of an inch in length, very clear, 

 granular, and brittle, so that when they break, they often 

 have abruptly rounded or square extremities. Each fibre- 



Fig. i55- : 



I. I 



cell possesses an elongated nucleus, and many are marked 

 along the middle, or, more rarely, along one of the edges, 



"" Fig. 155. Muscular fibre-cells from human arteries, magnified 

 350 diameters (Kolliker). a, natural state ; 5, treated with acetic 

 aci<J. 



f Fig. 156. Plain muscular fibres from the human bladder, mag- 

 nified 250 diameters. , in their natural state ; &, treated with acetic 

 ncid to show the nuclei. 



