714 MICTURITION. [BOOK n. 



being made for minor differences between man and other animals 

 in the anatomical arrangements. 



In the cat fibres carrying motor impulses for the bladder run in 

 the anterior roots of the 2nd and 3rd sacral nerves, possibly to some 

 extent in those of the 1st sacral or the 1st coccygeal, and reach the 

 bladder by the nervi erigentes and hypogastric plexus ; these are 

 medullated fibres which do not become connected with cells, and so 

 do not lose their medulla, until near their terminations. Other fibres 

 leave the spinal cord by the anterior roots of the 2nd, 3rd and 4th 

 lumbar nerves, possibly by those of the 1st or the 5th lumbar 

 nerves, and running in the rami communicantes to the lumbar 

 sympathetic chain, pass thence to the inferior mesenteric ganglion, 

 and so by the hypogastric nerves to the hypogastric plexus 

 (Fig. 90*). Most of these fibres become connected with cells 

 in the inferior mesenteric ganglion, and there losing their medulla 

 are continued on as non-medullated fibres. 



It has been maintained that the impulses passing by the sacral 

 fibres cause contractions of the longitudinally disposed muscular 

 fibres, and that those passing along the lumbar fibres and sympa- 

 thetic system cause contractions of the circularly disposed muscular 

 fibres ; and it has been further maintained that the former inhibit 

 the circularly disposed fibres and relax or open the 'sphincter,' 

 while the latter inhibit the longitudinally disposed fibres and 

 close the sphincter. But it is urged by other observers that 

 while there is a difference between the two sets in that the con- 

 tractions brought about by means of the sacral fibres are by far 

 the more powerful and have as well a greater tendency to be uni- 

 lateral, no such marked distinction in character as that stated 

 above exists. 



We may here incidentally remark that the sympathetic nerve 

 supply to the bladder affords the rare instance of a sympathetic 

 ganglion acting apparently as a reflex centre. If all the connections 

 of the inferior mesenteric ganglion with the spinal cord be severed 

 and one hypogastric be divided, stimulation of the central end of 

 the divided hypogastric will cause in many instances a contraction 

 of the bladder ; the impulses ascending the one hypogastric nerve 

 are reflected in the ganglion down the other hypogastric nerve. 

 This may be called a reflex act, but it probably differs in essential 

 nature from a reflex act, even a simple one, carried out by the 

 central nervous system. 



428. We said just now " when the bladder has become full," 

 but this must not be understood to mean, " when the bladder has 

 received a certain quantity of fluid." On the contrary, it is a matter 

 of common experience that we feel the desire to make water some- 

 times when a large quantity and sometimes when a small quantity 

 of urine has accumulated in the bladder. We have evidence that 

 the bladder possesses to a very high degree that obscure con- 

 tinuous contraction which we speak of as ' tone' ; and further that 



