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TEXT-BOOK OF PHYSIOLOGY 



Walking is a complicated act involving almost all the voluntary muscles 

 of the body either for purposes of progression or for balancing the head and 

 trunk, and may be defined as a progression in a forward horizontal direction 

 due to the alternate action of both legs. In walking one leg becomes for the 

 time being the active or supporting leg, carrying the trunk and head; the 

 other the passive but progressing leg, to become in turn the active leg when 

 the foot touches the ground. Each leg is therefore alternately in an active 

 and in a passive state. 



Running is distinguished from walking by the fact that at a given moment 

 both feet are off the ground and the body is raised in the air. 



THE VISCERAL OR INVOLUNTARY MUSCLE 



The visceral muscle, as the name implies, is found in the walls of hollow 

 viscera, where it is arranged in the form of a membrane or sheet. It is 

 present in the walls of the alimentary canal, blood-vessels, respiratory tract, 

 ureter, bladder, vas deferens, uterus, fallopian tubes, iris, etc. In some 

 situations it is especially thick and well developed e.g., uterus and pyloric 

 end of the stomach; in other situations it is thin and slightly developed. 



FIG. 39. Two SMOOTH MUSCLE-FIBERS FROM SMALL INTESTINE OF FROG. X 240. 

 Isolated with 35 per cent, potash-lye. The nuclei have lost their characteristic form through 

 the action of the lye. (Stohr.) 



The Histology of the Visceral Muscle-fiber. When examined with 

 the microscope, the muscle sheet is seen to be composed of fibers, narrow, 

 elongated, and fusiform in shape. As a rule, they are extremely small, 

 measuring only from 40 to 250 micromillimeters in length and from 4 to 8 

 micromillimeters in breadth. The center of each fiber presents a narrow, 

 elongated nucleus. The muscle-protoplasm which makes up the body of 



the fiber appears to be enclosed by a 

 delicate elastic membrane resembling in 

 some respects the sarcolemma of the 

 skeletal muscle. In some animals the 

 visceral fiber presents a longitudinal 

 striation suggesting the existence of fib- 

 rillae surrounded by sarcoplasm (Fig. 39). 

 The fibers are united longitudinally and 

 FIG. 40. SECTION OF THE CIRCULAR tran5vpr5plv u v o rpr npn1- material The 

 LAYER OF THE MUSCULAR COAT OF THE transversely by a ceme 

 HUMAN INTESTINE. (Stohr.}\ muscle is increased in thickness by the 



superposition of successive layers. At 



varying intervals the fibers are grouped into bundles or fasciculi by septa 

 of connective tissue (Fig. 40). Blood-vessels ramify in the connective tissue 

 and furnish the necessary nutritive material. 



The visceral muscle receives stimuli from the spinal cord, not directly, 

 however, as in the case of the skeletal muscle, but indirectly through the 

 intermediation of ganglion cells, which may be located at some distance 

 from the muscle or near the walls of the viscera. Non-medullated fibers 



Connecti ve-tissu e_ 

 septum. 



Nucleus 



Smooth muscle-fib 

 in transverse section 



