98 TEXT-BOOK OF PHYSIOLOGY. 



longitudinally and transversely by a cement material. The 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 



FIG. 39. TVo 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.) 



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 from the ganglion pass directly into the 

 muscle, where they frequently unite to form a general plexus. From 

 this. plexus fine branches take their origin and ultimately become 

 physiologically associated with the muscle-fiber. 



Physiologic Properties. The visceral muscles which have 

 been subjected to experiment are mainly those of the stomach, in- 

 testine, bladder, ureter, and iris. From the results of the experiments 



which have been published, it is 

 evident that all visceraJLjnuscles 

 possess elasticity. tonicity._irrita- 

 bilitv T and conductivity. 



The elasticity of the bladder 

 muscle of the cat w r as strikingly 

 shown in the experiments pub- 

 lished by Dr. Colin C. Stewart. 

 When this muscle was weighted 

 with weights differing by a com- 

 mon increment, it w r as extended 

 on the addition of each weight, 

 though to a progressively less extent. On the removal of the weights 

 the muscle eventually returned to its former length. The records of 

 the extension were similar to, if not identical with, those of the skele- 

 tal muscle. 



Tonicity is a property common to all visceral muscles. Each 

 muscle is continuously in a state of contraction intermediate between 

 that of complete contraction and that of relaxation. In how far this 

 is due to local and inherent causes or to stimuli reflected from the 



Connective-tissue 

 septum . 



Nucleus. 



Smooth muscle-fiber 

 in transverse section. 



FIG. 40. SECTION OF THE CIRCULAR 

 LAYER OF THE MUSCULAR COAT OF 

 THE HUMAN INTESTINE. (Stohr.) 



