DEFECATION. 337 



The upper set of fibres pass into the lumbar sympathetic chain, and 

 thence in the mesentery to the inferior mesenteric ganglia, and so by 

 the colonic and hypogastric nerves to the rectum. .They are connected 

 with nerve cells chiefly in the inferior mesenteric ganglia, and supply 

 the descending colon, rectum, and internal sphincter. A few fibres 

 pass along the sympathetic chain to the sacral ganglia, and thence by 

 the grey rami of the ganglia to the sacral nerves ; in these they follow 

 the somatic branches of the sacral nerves, and end chiefly in the 

 unstriated muscles of the skin round the anus. 



The lower set of fibres run in the pelvic nerves, or nervi erigentes. 

 They pass into the hypogastric plexus, and have ganglion cells either as 

 they pass the side of the rectum, or more peripherally. 



The object or use of this double nerve supply to the rectum is 

 difficult to ascertain. It is natural to imagine that these two sets of 

 nerve fibres should be antagonistic to one another, as is the case with 

 other organs, such as the heart, which are supplied with nerves from 

 two sources. Fellner, working in v. Basch's laboratory, has indeed 

 come to the conclusion that the theory of " crossed innervation," put 

 forward by the latter, also applies to the rectum. According to tkis 

 theory, when a muscular tube containing circular and longitudinal 

 fibres in its walls, is supplied with two sets of nerve fibres, one set of 

 nerves will be inhibitory for the longitudinal and motor for the circular 

 muscles, while the other nerves will be motor for the longitudinal and 

 inhibitory for the circular muscles. Fellner, 1 as the result of experi- 

 ments on the dog, concluded that the sacral nerves are motor for the 

 longitudinal muscles of the rectum, including the recto-coccygeal muscle, 

 and inhibitory for the circular muscles, whereas the fibres which run 

 from the hypogastric nerves cause contraction of the circular fibres 

 and relaxation of the longitudinal. We have already seen that this 

 theory is inadmissible for the intestine, and Langley and Anderson, while 

 not denying the possible accuracy of Fellner's experiments, so far as the 

 rectum of the dog is concerned, have shown that they do not apply to 

 other animals. In rabbits and cats they find that the fibres from the 

 lumbar nerves may cause either inhibition or contraction of either 

 muscular coat. The usual result was inhibition of both coats of the 

 rectum, which might be preceded or followed by a slight contraction. 

 On the internal sphincter the effects were again variable, though here 

 also inhibition predominated. 



Excitation of the sacral nerves produced much more marked 

 results than did that of the hypogastric nerves. In most cases a 

 strong contraction of the recto-coccygeal muscle and of the longitudinal 

 fibres of the rectum was accompanied by marked relaxation- and 

 dilatation of the internal sphincter. Strong peristaltic contractions 

 were also set up in the lower part of the bowel, so that stimulation of 

 these nerves gave rise to defoecation. Here, therefore, both kinds of 

 fibres were caused to contract in the upper part of the rectum. In a 

 few cases the relaxation of the internal sphincter was replaced or 

 succeeded by a contraction of this muscle. 



The voluntary external sphincter and levator ani are also supplied 

 from the sacral nerves ; in man, from the fourth sacral. 



1 Med. Jahrb., Wien, 1883, S. 571, and Arch. f. d. ges. Physiol., Bonn, 1893, Bd. Ivi. 

 S. 542. The tracings given in the latter paper do not, however, by any means support 

 Fellner's contentions. 

 VOL. II. 22 



