THE EXPULSION OF THE URINE. MICTURITION 1079 



the bladder, and, on the other, to a relaxation of the sphincter, two 

 separate nerve paths must be provided for. According to Langley 

 and Anderson, 1 one of these arises in the four upper lumbar nerves and 

 the other, in the second and third sacral nerves by way of the visceral 

 nerves of the pelvis, the nervi erigentes. The former eventually termi- 

 nate in the bilateral inferior mesenteric ganglion, whence a new relay 

 of fibers is formed which extends in the form of two nerves, the hypo- 

 gastric nerves, into the pelvis on each side of the rectum. They termi- 

 nate finally at the base of the bladder in an extensive ramification 

 which is known as the hypogastric plexus. From here these fibers 

 ascend to the fundus of the bladder. The second set of fibers passes 

 from the second and third sacral nerves directly to the hypogastric 

 plexus, and hence, they do not first enter the sympathetic system. 

 Their relay stations lie in the aforesaid plexus and in the walls of the 

 bladder itself. The afferent impulses from this organ select chiefly 

 these visceral fibers of the pelvis in reaching central parts. ^ 



This brief enumeration shows that the hypogastric plexus is sup- 

 plied with sympathetic fibers from the lumbar cord and with para- 

 sympathetic fibers from the sacral cord. As far as the individual 

 action of these fibers is concerned, further investigations are needed to 

 be able to cite definite results. All physiologists, however, are agreed 

 that the excitation of the sacral fibers on either side produces a strong 

 contraction of the bladder, leading to the relaxation of the sphincters 

 and the discharge of the urine. But, the question whether these 

 nerves actually contain inhibitory fibers for the sphincters, has not been 

 definitely settled. Fagge,^ for example, claims that they do not and 

 that the relaxation of the sphincters takes place indirectly in conse- 

 quence of the high intrave^cal pressure. The function of the hypo- 

 gastric nerves has not been clearly established, because it is not the 

 same in all animals. In the dog, their stimulation leads to a strong 

 contraction of the musculature around the base of the bladder, whereas 

 in the cat and rabbit this procedure gives rise to an inhibition. It 

 appears, however, that they are never without motor fibers for the 

 sphincter vesicae and the constrictor tissue of the urethra. 



1 Jour, of Physiol., xix, 1895, 71; also Stewdrt, Am. Jiour. of Physiol., xxx, 

 i. 



2 Nawrocki and Skabitschewsky, Pfliiger's Archiv, xlix, 1891, 141. 



3 Jour, of Physiol., xxviii, 1902, 305. 



