THE MUSCLES. 



The study of the muscular system is known as myology. 

 The muscles are of two kinds : voluntary, which are under 

 the control of the will; and involuntary, which cannot be 

 controlled by the will. All muscles moving the bones are 

 voluntary and are supplied with branches of the cerebro- 

 spinal nerves. Examples of involuntary muscles are 

 found in the walls of the alimentary canal, the ureter, 

 bronchial tubes, and blood-vessels. These are supplied 

 with nerves from the sympathetic nervous system (Fig. 

 91). The structure of a voluntary muscle may be seen 

 by teasing a small piece on a slide in a drop of water, 

 covering with a cover-glass, and examining with the 

 compound microscope. It is composed of striated fibers 

 from one to fifteen centimeters in length, w r hile involun- 

 tary muscle is composed of cells more or less spindle- 

 shaped and non-striated, except in the heart (Figs. 8 

 and 10). 



There are over five hundred voluntary muscles in the 

 cat, each of which is usually attached at either end to 

 the periosteum of a bone. That point of attachment 

 which is the center of motion is known as the origin of 

 the muscle, and is usually more proximad than the 

 insertion of the muscle. In the case of the biceps, its 

 origin is on the scapula and its insertion on the radius. 

 Usually a muscle originates and terminates in a white 

 glistening cord called a tendon, composed for the most part 

 of white fibrous tissue (Fig. n). 



Each muscle-fiber is surrounded by a transparent 



93 



