1078 



EXCRETION 



and various afferent impulses may be brought to bear upon this reflex 

 mechanism. Thus, we have previously found that micturition may 

 also be evoked by associations resulting in consequence of visual and 

 auditory impressions, such as the sight or sound of running water. 

 Secondly, the action of the simple center may be inhibited or accelerated 

 by volition. In the latter case, however, the impulses seem to be con- 

 centrated upon the sphincter mechanism and upon those perineal mus- 

 cles which normally aid in the closure of the urethra. Contrariwise, 



BttD. me*, ganglion. 



Sup. mes. nerves 



Median mes. nerves 



Inf. mes. nerves 



Inf. mes. ganglior. 



-- 3rd Iamb, vert, 



Eectum--- 



BUddei 



Femui 



Ischiun. \- 



Urethra ,._ 



- --llypogastric 



plexus 

 Sacrum 



. . ..Sciatic n. 

 .Sacral nerves 



FIG. 526. NERVE SUPPLY TO BLADDER OF CAT. (Nawrocki and Skabilschewsky.) 



the relaxation of these sphincters may be hastened by the con- 

 traction of the abdominal muscles; in fact, it is held by some investi- 

 gators that even the involuntary muscle tissue of the bladder is partially 

 under the control of the cortex of the cerebrum. This view is based 

 upon the fact that the destruction of the crus cerebri in animals whose 

 abdomen had been opened, gives rise to a contraction of the bladder. 

 Since the local mechanism of micturition requires efferent impulses 

 which, on the one hand, lead to a contraction of the musculature of 



