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 



/ Q ^9 '4^ 1^ 



from the sympathetic nervous system (Fig$ 9*). 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 centi- 

 meters in length, while involuntary 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 peri- 

 osteum of a bone. The point of attachment on the un- 

 moved bone is known as the origin of the muscle. The 

 insertion of a muscle is its attachment to the bone which 

 it moves. 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 tis- 

 sue (Fig. n). 



Each muscle-fiber is surrounded by a transparent elastic 

 sheath, the sarcolemma. A number of fibers bound together 

 by a loose connective tissue, and the whole enveloped by an 

 extension of the same, is a fasciculus. The tissue connect- 



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