MICTURITION 393 



dominal pressure plays no essential part in micturition, and unaided is not 

 sufficient to empty the bladder. 



The bladder receives its motor nerves in part from the lumbar, in part 

 from the sacral nerves (Fig. 145). The former in the dog emerge in the 

 second to fourth lumbar roots and run through the lumbar part of the sym- 

 pathetic., the mesenteric nerves, the inferior mesenteric ganglion, the hypo- 

 gastric nerves and the hypogastric plexus to the vesical plexus. The sacral 

 nerves arise from the second to fourth sacral roots, and pass in the nervi erri- 

 gentes, through the hypogastric plexus to the plexus of the bladder. 



Both the circular and the longitudinal muscle fibers are supplied through 

 these nerv.es; action extends in part also to the opposite side, so that the 

 function of the bladder is not impaired if the nerves of one side only are 

 uninjured. 



According to v. Zeissl, Rehfisch, and others, the sphincter of the bladder is 

 relaxed by stimulation of the nervus errigens; C. Stewart has observed also a 

 relaxation of the contracted bladder under the influence of these nerves. Such 

 an inhibiting effect, however, is positively denied by other authors. 



A bilateral center for the control of the bladder is located in the lumbar 

 cord (Goltz). Each half of this center has control of the entire bladder. 

 Besides, the higher parts of the central nervous system exert an influence on 

 the bladder. Contractions (in the cat) are obtained by stimulation of the 

 anterior portion of the sigmoid gyms of the cerebrum. The,, conducting path- 

 way is said to pass through the thalamus, the crura cerebri, the pons and 

 the medulla to the spinal cord. In the cord the paths traverse the posterior 

 section of the lateral columns, and are direct as far as the lumbar cord (and 

 the inferior mesenteric ganglion) where they undergo a partial crossing (C. 

 Stewart). 



These centers are roused by various reflex influences., contractions of the 

 bladder having been observed as the result of stimulation of all kinds of 

 afferent nerves except the vagus. Of still greater interest are the true afferent 

 nerves from the bladder which reach the cord mainly by the second and third 

 posterior sacral roots. The reflex center lies between the third and fifth 

 lumbar roots, and the sacral nerves to the bladder only contain the efferent 

 fibers. Contractions are reflexly produced also by stimulation of the central 

 end of the hypogastric nerves, the inferior mesenteric ganglion in this case 

 assuming the role of a reflex center (Xawrocki and Skabitschewsky ; cf., 

 however, " axon reflex" in Chapter XXII). 



The bladder is not absolutely dependent on the cooperation of the central 

 nervous system in carrying out its movements. Dogs, whose spinal cord was 

 extirpated below the thoracic portion, showed at first a greater or less dis- 

 turbance of the bladder function, but the condition gradually improved, the 

 urine was expelled spontaneously and in larger quantities at a time, and 

 after some months micturition was performed in a manner perfectly adequate 

 for the continuance of health (Goltz and Ewald). 



Under normal circumstances the urine in the bladder does not undergo any 

 visible changes, either by diffusion or absorption. Even with forced retention 

 of the urine diffusion is too slight to be held responsible for any of the symptoms 

 accompanying that condition. 



