DISTRIBUTION AND ACTION OF NERVE FIBRES. 667 



always sends a considerable number of fibres to the pelvic nerve, and 

 the third generally does ; the first sends comparatively few fibres, and 

 none when the arrangement of nerves is posterior. In the rabbit, the 

 pelvic nerve arises chiefly from the third and fourth sacral nerves, the 

 second sacral nerve also sending fibres to it in the anterior and median 

 classes ; the first coccygeal nerve sending some fibres to it in the posterior 

 class. 



Stimulation of the pelvic nerve 1 causes strong contraction of the 

 bladder, but has no certain effect on the blood vessels of the organ ; it 

 causes contraction, varying in strength, of both coats of the descending 

 colon and rectum, the effect being much more constant, and generally 

 greater, in the rabbit than in the cat and dog ; strong contraction of the 

 recto-coccygeal muscle and of other special longitudinal muscles of the 

 rectum ; dilatation of the vessels of the mucous membrane of the end of 

 the rectum, and of the external generative organs; inhibition of the 

 proper unstriated muscle of the external generative organs, notably 

 of the retractor penis ; inhibition in the rabbit of the internal anal 

 sphincter, and of some unstriated muscle in the skin of the ano-genital 

 region. 



It has been commonly said that the pelvic nerve contains motor 

 fibres for the uterus. Anderson and myself 2 in numerous experiments 

 found the pelvic nerve and the sacral nerves to be entirely ineffective 

 on the uterus. Further, section of the sacral nerves 3 in the cat or 

 rabbit caused no degeneration in nerve fibres running to the uterus or 

 to the vagina, though it caused considerable degeneration in the strands 

 running to the rectum and bladder, and some in the strands to the 

 urethra and vulva; and we concluded that the sacral nerves do not 

 send nerve fibres to the internal generative organs. It is, however, 

 possible that some of the afferent fibres which run to the vulva may 

 run on past this structure, and it is to be remembered that human 

 anatomists have described filaments as passing from the sacral nerves to 

 the uterus. 



The origin from the spinal cord of the nerve fibres to the several 

 viscera supplied by the pelvic nerve, is in correspondence with the 

 anatomical origin of the nerve, stated above, except that the nerve fibres 

 to the external generative organs are rather more anterior than those 

 to the bladder and the end of the intestine. 



The pelvic nerve soon breaks up into a plexus of nerve fibres 

 containing numerous small ganglia. In these, the nerve fibres end. 

 Speaking broadly, the ganglia in the neighbourhood of each organ are on 

 the course of the fibres for that organ 4 (cf. Fig. 314). Thus, in the rabbit, 

 after injection of nicotin, the pelvic nerves have no effect, but on stimu- 

 lating the peripheral parts of the plexus all the usual effects are obtained. 



The pelvic nerve consists chiefly of small medullated fibres, but both 

 medium and large fibres are present ; it has near its origin few or no 

 non-medullated fibres. 



In the cat, the pelvic nerve contains 5 about 3500 medullated fibres. Of 

 these, one to two dozen are 7 /a to 12 /x in diameter; several hundreds, 4 //. to 



1 Cf. Langley and Anderson, Jowrn. Physiol., Cambridge and London, 1895, vol. xviii. 

 p. 67 ; vol. xix. pp. 72, 85, 122. References to earlier observations are given in these papers. 

 - Ibid., 1895, vol. xix. p. 122. 



3 Ibid., 1895, vol. xix. p. 372 ; vol. xx. p. 379. 



4 Langley and Anderson, ihid., 1895, vol. xix. p. 131. 



3 Langley and Anderson, ibid., 1895, vol. xix. p. 377. 



