28 ANATOMY. 



Structure. — The voluntary muscle consists of bundles of 

 bundled fibers, each individual fiber has its own delicate sheath. 

 A number of fibers are enclosed within a common connective tis- 

 sue sheath and constitute a minute bundle. A number of these 

 bundles are in turn wrapped within a connective tissue sheath, 

 forming a larger bundle. These larger bundles may in turn be 

 wrapped by means of another connective tissue sheath into a still 

 larger bundle. 



The voluntary muscle fiber is long, threadlike, marked by 

 cross stripes which are very close together, and may end in ten- 

 don fiber. These muscle fibers are about 1-1500 of an inch wide, 

 but may be very long. 



Involuntary muscles. — Involuntary muscle fibers are merely 

 long, spindle shaped cells, which do not end in tendon fibers. 

 They may be arranged in the form of small bundles and are usu- 

 ally in the form of thin sheets. Involuntary muscle tissue is light- 

 er in color than voluntary and usually encloses hollow organs 

 forming one of the coats or layers. The middle coat of the stom- 

 ach and intestines is composed of involuntary muscle fibers. 



Function. — It is their function to carry on work which could 

 not be entrusted to conscious control and with which the brain 

 could not well be burdened. 



Peristaltic action of the stomach and intestines is produced 

 by the rythmic action of these muscle fibers. The heart muscle 

 fibers differ from both the typical voluntary and the typical in- 

 voluntary fibers. They are striped but operate independently of 

 the will. 



Source of heat and power.— Muscular power comes from ox- 

 idation of food material in the various tissues of the body, par- 

 ticularly in the muscles and larger glands. During the process 

 of oxidation, carbonic gas and other materials are developed. 

 Power is increased by proper nourishment, and is decreased by 

 lack of nourishment. Muscles lose in strength l)y over work be- 

 cause they are consumed more rapidly than rebuilt. Muscles 

 are paired in a double sense. The rule is that for any given 

 muscle there is a corresponding muscle on the other side of the 

 body and also one or more opposing muscles on its own side. 



The belly of a muscle has a rich blood supply ; the tendon has 

 very little. 



