864 PHYSIOLOGY OF DIGESTION AND SECRETION. 



tractions which move in both directions from the point stimulated. 

 He was not able to find ganglion cells in the upper two-thirds of the 

 ureter and was led to believe, therefore, that the contraction orig- 

 inates in the muscular tissue independently of extrinsic or intrinsic 

 nerves, and that the contraction wave propagates itself directly 

 from muscle cell to muscle cell, the entire musculature behaving 

 as though it were a single, colossal, hollow muscle-fiber. Efforts 

 to show a regulatory action upon these movements through the 

 central nervous system have so far given negative results. 



Movements of the Bladder. The bladder contains a muscular 

 coat of plain muscle tissue, which, according to the usual descrip- 

 tion, is arranged so as to make an external longitudinal coat and an 

 internal circular or oblique coat. A thin, longitudinal layer of 

 muscle tissue lying to the interior of the circular coat is also de- 

 scribed. The separation between the longitudinal and circular 

 layers is not so definite as in the case of the intestine; they seem, 

 in fact, to form a continuous layer, one passing gradually into the 

 other by a change in the direction of the fibers. At the opening of 

 the bladder into the urethra, the musculature in the submucosa is 

 strengthened to form a ring around the orifice and along the begin- 

 ning of the urethra which is supposed to function as a sphincter, the 

 internal sphincter or sphincter vesicce internus. Around the urethra, 

 in the prostate and membranous portions, is a circular layer of 

 striated muscle that is frequently designated as the external 

 sphincter or sphincter urethrae. The urine brought into the 

 bladder accumulates within its cavity to a certain limit. It is 

 prevented from escaping through the urethra by a tonic contrac- 

 tion of the internal sphincter. When the accumulation becomes 

 greater the external sphincter may be brought into action. Back- 

 flow of urine from the bladder into the ureters is effectually pre- 

 vented by the oblique course of the ureters through the wall of 

 the bladder. Owing to this circumstance, pressure within the blac^- 

 der serves to close the mouths of the ureters, and, indeed, the more 

 completely, the higher the pressure. At some point in the filling 

 of the bladder the pressure is sufficient to arouse a conscious sen- 

 sation of fullness and a desire to micturate. Under normal condi- 

 tions the act of micturition follows. It consists essentially in a 

 strong contraction of the bladder, with a simultaneous relaxation 

 of the internal sphincter, and of the external sphincter also if this 

 latter is in contraction. 



The force of this contraction is considerable, as is evidenced by 

 the height to which the urine may spurt from the end of the urethra. 

 According to Mosso, the contraction may support, in the dog, a 

 column of liquid two meters high. The contractions of the blad- 

 der may be and usually are assisted by contractions of the walls 



