vi INTESTINE AS AN OEGAN OF EXCKETION 371 



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system. The former are branches of the lumbar and sacral nerves, 

 the latter of the inferior mesenteric plexus and the hypogastric 

 plexus (see Fig. 83, p. 247). The sensory fibres from this last 

 plexus cause the excessive sensibility of the mucous membrane of 

 the rectum and anus, and its motor fibres discharge the movements 

 of defaecation. The hypogastric rami from the lumbar cord run in 

 the same plexus after traversing the inferior mesenteric plexus, 

 along with the fibres from the 

 anterior roots of the first and 

 second sacral nerves, which under 

 the name of the nervus erigens 

 (Eckhard) innervate the corpora 

 cavernosa, and give off the nervus 

 pudendus, from which the haemor- 

 rhoidal rami run to the sphincters 

 of the anus (Figs. 105 and 106). 



The closure of the ileocaecal 

 valve is also effected by nervous 

 action (Katz and Winkler, 1902). 

 Stimulation of the central end of 

 the sciatic relaxes the closed valve, 

 or brings it to, if previously open. 

 Stimulation of the vagus usually 

 produces closure of the splanchnic 

 opening. The nervi erigentes and 

 the hypogastrics are ineffective, so 

 that its innervation again shows 

 the ileocaecal valve to belong to the 

 small intestine. 



The question already discussed 

 in Chapter IV. (p. 265 et seq.) as to 

 the simultaneous or alternate action 

 of the longitudinal or circular 

 fibres of the small intestine, comes 

 up again in relation to the 

 muscles of the colon and rectum. 

 Certain experimenters (Courtade 



and Guyon, 1897) stated that electrical stimulation of the 

 sympathetic rami in the dog produces contraction of the circular 

 fibres of the colon, rectum, and anus, and inhibits the contraction 

 of the longitudinal fibres ; vice versa, stimulation of the sacral 

 nerves contracts the longitudinal and inhibits the circular fibres, 

 including those of the sphincter. There would thus be a functional 

 antagonism between the two orders of nerves. On the other 

 hand, Langley and Anderson (1895-96), experimenting on the 

 rabbit, state that stimulation of the sacral nerves throws both 

 longitudinal and circular muscles into contraction, while stinmla- 



FIG. 10(3. Schema of nerves which arise (in 

 dog) from last part of lumbar cord, and 

 in sacral cord. (Frangois-Franck.) Sa, 

 os sacrum ; 5L, 6L, 7L, lumbar vertebrae ; 

 N.sc, sciatic nerve ; N. e, nervous erigens 

 from 1 and 2 sacral nerves (IS, %S) ; N. p, 

 nervous pudendus ; C. e, cauda equina. 



