MUSCLE STRUCTURE 83 



the food and the air upon which their life depends come only 

 through the aid of those constant workers, the muscles. All 

 motion of any sort in the body, whether conscious or unconscious, 

 is due to their action. If the motion is voluntary it is due to 

 muscles which are controlled by the will, or voluntary muscles. 

 Muscles which cannot be controlled by the will are involuntary; 

 they are found in the internal organs of the body, or the viscera, 

 and in the coats of vessels. All other muscles are voluntary, and 

 since they are attached to bones they are called skeletal muscles. 



Contractile tissues: Muscular and ciliated epithelial cells. 

 Striped skeletal muscle. 

 Striped cardiac muscle. 

 Unstriped visceral muscle. 



STRUCTURE OF MUSCLES 



Muscles consist chiefly of collections of red fibers, each fiber 

 composed of little bundles of muscle-cells. All of these are 

 wrapped in connective tissue, bound together and enclosed in a 

 sheath. 



Transition zone. 





Nucleus tendon. Z 



FIG. 71. LONGITUDINAL SECTION OF A PART OF A MUSCLE FIBERVFROM A 

 HUMAN INTERNAL INTERCOSTAL MUSCLE, SHOWING ITS TRANSITION TO TENDON. 

 X 750. (Lewis and St'dhr.) 



Examining a muscle with care, we can strip off the sheath of connective 

 tissue (epi-mysium) , and we shall find that it sends layers down into the 

 muscle to form septa or partitions (peri-mysium) enclosing the bundles (or 

 fasciculi) of which the muscle is made up. 



With the aid of the microscope the fiber cells which compose the bundles 

 are revealed, surrounded by still more delicate connective tissue (endo- 

 mysium). 



Also, under the microscope the fiber cells of voluntary muscle tissue ap- 

 pear striped, consequently voluntary muscle is said to be striped or striated. 

 Involuntary fiber cells are plain involuntary muscle is unstriped or non- 

 striated. This sort of muscle is found in internal organs, whose work must go 

 on continually without our conscious supervision. 



