348 MECHANISMS OF THE GENERATIVE APPARATUS. 



position of this organ, so that its axis more nearly coincides with that 

 of the vagina, and, according to observations on animals, in an active 

 antiperistaltic contraction of uterus and Fallopian tubes, by which the 

 semen becomes forwarded towards the ovaries. Some such movement 

 as this seems necessary to explain the fact that the fertilisation of the 

 ovum takes place, as a rule, in the Fallopian tubes, and may take place 

 on the surface of the ovaries or in the abdominal cavity. 



Nervous mechanism. Although, in both sexes, coitus is attended 

 by a high degree of psychical excitement, yet it is essentially a reflex 

 act, and can be carried out when all impulses from the higher centres 

 are cut off by section of the cord in the dorsal region. The centre 

 presiding over the act is situated in the lumbar spinal cord ; and we 

 have now to consider the paths, afferent and efferent, which are con- 

 cerned in the various phases of the act. 



The first accurate information on these points was furnished by the 

 discovery by Eckhard l of the function of the iiervi erigentes. Since 

 this time, the nerves to the generative organs have been the subject of 

 investigation by Gaskell, 2 Morat, 3 Sherrington 4 and Langley and 

 Anderson. 5 I shall follow the very full account given by the two last- 

 named observers. 



The external generative organs, like the bladder, are supplied from 

 two sets of nerve fibres from the lumbar nerves through the sym- 

 pathetic, and from the sacral nerves. The fibres from the lumbar 

 nerves arise in the cat from the second, third, and fourth, or the third, 

 fourth, and fifth lumbar nerve-roots, and in the dog from the thirteenth 

 thoracic, and the first to the fourth lumbar roots. They run in the 

 white rami communicantes to the sympathetic chain, whence they may 

 take two paths. 



(a) The great majority of the fibres run down the sympathetic 

 chain to the sacral ganglia, whence fibres are given off in the grey rami 

 communicantes to the sacral nerves; their further course is by the 

 pudic nerves, none running in the nervi erigentes. 



(b) A few fibres go by the hypogastric nerves to the pelvic 

 plexus. 



Excitation of these fibres causes strong contraction of the arteries 

 of the penis, and of the unstriated muscles of the tunica dartos of the 

 scrotum. In animals which possess a retractor penis muscle, excitation 

 of the lumbar nerves causes strong contraction of the muscle. 



The fibres from the sacral nerve can be divided into two classes 

 visceral and somatic. The visceral branches run in the pelvic nerves, 

 or nervi erigentes. Stimulation of these fibres produces active dilata- 

 tion of the arteries of the penis or vulva, and also inhibition of the 

 unstriated muscle or body of the penis, the retractor muscle of the 

 penis, when present, and of the vulva muscles. The somatic branches 

 supply motor nerves to the ischio- and bulbo-cavernosi, as well as the 

 constrictor urethrse. In the female, they supply the analogous muscles, 

 namely, the erector clitoridis (ischio-cavernosus), and the sphincter 

 vaginae (bulbo-cavernosus). Both these sets of fibres are therefore in- 

 volved in the erection of the generative organs which accompanies coitus. 



1 Beitr. z. Anat. u. Physiol. (Eckhard), Giessen, 1866. 



2 Journ. Physiol., Cambridge and London, 1886, vol. vii. p. 1. 



3 Arch, de physiol. norm, etpath., Paris, 1890, tome ii. 



4 Journ. Physiol., Cambridge and London, 1892, vol. xiii. p. 675. 



5 Ibid., 1895, vol. xix. p. 85. 



