Chap. VI.] 



THE MUSCLES. 



55 



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 plentifully supplied with blood-vessels. 



The muscular fibres lie closely packed, their ends lapping 

 over on to adjacent fibres, and forming bundles. These bundles 

 are grouped so as to make 

 larger bundles, and in this 

 way the muscles which are 

 attached to the skeleton are 

 formed. 



Involuntary, non-striated mus- 

 cular tissue is composed of 

 long, somewhat flattened, 

 elongated fibre-cells. Each 

 fibre-cell contains an oval or 

 rod-shaped nucleus, contain- 

 ing one or more nucleoli. 

 The substance of the fibre- 

 cell is longitudinally striated, 

 but does not exhibit trans- 

 verse striation. The fibre- 

 cells lie side by side, or lap 

 over one another at the ends, 

 and are joined together by a 

 small amount of cement sub- 

 stance. 



This kind of muscular tis- 

 sue is found arranged around 

 the blood-vessels and most 

 of the hollow viscera. The 

 fibres are variously grouped 

 in different parts of the body ; 

 sometimes crowded together 

 in solid bundles, which are arranged in layers and surrounded 

 by connective tissue, as in the intestines ; sometimes arranged 

 in narrow interlacing bundles, as in the bladder ; sometimes 

 wound in single or double layers around the blood-vessels ; and 

 again, running in various directions and associated with bands 

 of connective tissue, they form large compact masses, as in the 

 uterus. 





Fig. 5'.>. — Wave of ('<intr action pass- 

 ing OVER A Muscular Fibrk of Dytiscus. 

 Very highly magnified. B, R, portions 

 of the fibre at rest; C, contracted part; 

 /, I, intermediate condition. 



