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 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 ro). 
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. 11). 
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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