866 PHYSIOLOGY OF DIGESTION AND SECRETION. 



happens that we have sometimes a strong desire to micturate when 

 the bladder contains but little urine, for example, under emotional 

 excitement. In such cases if the micturition is prevented, probably 

 by the action of the external sphincter, the bladder may sub- 

 sequently relax and the sensation of fullness and desire to micturate 

 'pass away until the urine accumulates in sufficient quantity, or the 

 pressure is again raised by some circumstance which causes a reflex 

 contraction of the bladder. 



Nervous Mechanism. According to Langley and Anderson,* the 

 bladder in cats, dogs, and rabbits receives motor fibers from two 

 sources: (1) From the lumbar nerves, the fibers passing out in the 

 second to the fifth lumbar nerves and reaching the bladder through 

 the sympathetic chain and the inferior mesenteric ganglion and 

 the hypogastric nerves and plexus (Fig. 287). Stimulation of 

 these nerves causes a comparatively feeble contraction of the blad- 

 der followed by an inhibition. (2) From the sacral spinal nerves, 

 the fibers originating in the second and third sacral spinal nerves, 

 or in the rabbit in the third and fourth, and taking their course 

 through the so-called nervi erigentes or pelvic nerves and the hypo- 

 gastric plexus. Stimulation of these nerves causes strong contrac- 

 tions of the bladder, sufficient to empty its contents. (3) Experi- 

 ments in lower animals indicate that the urethra, in addition 

 to the paths just described, receives fibers also from the pudic 

 branch of the sciatic plexus. According to Nawrocki and Skabit- 

 schewsky,t the spinal sensory fibers from the bladder are found in 

 the posterior roots of the first, second, third, and fourth sacral 

 spinal nerves, particularly the second and third. When these 

 fibers are stimulated they excite reflexly the motor fibers to the 

 bladder found in the anterior roots of the second and third sacral 

 spinal nerves. The relations of this nerve-supply to the act of 

 micturition is difficult to state. That the act is essentially a reflex 

 through the central nervous system is shown by the fact that 

 section of the nervi erigentes or of the posterior roots of the 

 sacral spinal nerves abolishes the act and leads to a distention of 

 the bladder. As far as experiments have gone they indicate that 

 the motor path for this reflex lies through the nervi erigentes or 

 pelvic nerves, while the afferent paths enter the cord in the pos- 

 terior roots of the sacral spinal nerves, coming through the pelvic 

 or the pelvic and pudic nerves. The hypogastric nerve apparently 

 does not enter into the reflex, but its inhibitory influence upon the 

 bladder may, by relaxing the tone of the musculature, provide a 

 mechanism for holding larger quantities of urine. So far as the 

 bladder is concerned there is evidence that the hypogastrics and 



"Journal of Physiology," 19, 71, 1895. 

 "Archiv f. die gesammte Physiologic," 



