470 PHYSIOLOGY CHAP. 



Micturition without desire, therefore, differs from that caused 

 by desire only in the fact that the dilatation of the urethral orifice 

 by voluntary relaxation of the internal sphincter precedes instead 

 of following the reflex contraction of the detrusor. 



XI. It is very important that we should complete the study 

 of micturition by reviewing the experimental evidence for the 

 innervation of the bladder, since it substantially confirms our 

 theory as to the mechanism of micturition in the above three 

 different cases. 



From a number of experiments on dogs, cats, and rabbits, we 

 may assume positively that the bladder is supplied by two sets 

 of nerves. The first set are derived from the lumbar nerve-roots, 

 particularly from the third and fourth pairs, the fibres of which 

 run in the rami communicantes to the lumbar part of the sym- 

 pathetic chain, where with the mesenteric nerves (upper, middle, 

 and lower) they join the inferior mesenteric ganglion, and finally, 

 by the hypogastric nerves, reach the hypogastric plexus and the 

 bladder. 



The second set of nerves to the bladder originate in the roots 

 (both anterior and posterior) of the sacral nerves, especially of the 

 first to the second pair, from which two branches are given off, 

 known as the nervi erigentes of Eckhard, which run straight to 

 the hypogastric plexus, and thence to the bladder and the corpora 

 cavernosa of the penis (see Fig. 106, p. 371). So that all the 

 nerves which run from the cerebrospinal axis to the bladder pass 

 in two distinct nerve-trunks, the hypogastric and the nervus 

 erigens. Both, as we shall see, innervate the detrusor, and also 

 the internal sphincter of plain muscle. The external sphincter 

 and other striated muscles of the urethra are innervated by the 

 nervus pudendus (Griffiths). 



The vesical nerves are particularly abundant at the neck of 

 the bladder, where they form plexuses in which ganglion cells are 

 included (E. Mayer) : they terminate partly in the blood-vessels 

 (vasomotor nerves), partly in the muscle cells (motor nerves to 

 muscles), and partly penetrate between the layers of the epithelium 

 (sensory nerves). 



Budge (1864) was one of the first to investigate the motor and 

 sensory nerve -paths to the bladder. He saw that the nerves 

 coming from the anterior sacral roots are able to excite contraction 

 of the bladder directly, and also reflexly (by stimulation of corre- 

 sponding posterior roots). Stimulation of the lumbar sympathetic 

 also produced contraction of the bladder, but this was always 

 accompanied by signs of pain in the animal. Stimulation of the 

 central cord of this nerve produced the same effect. Section of 

 the rami communicantes so as to interrupt all connection with 

 the cord, but not with the hypogastric nerves and plexus, had, 

 according to Budge, no effect on the bladder. From this he 



