256 THE PHYSIOLOGY OF REPRODUCTION 



to confirm this statement, but they found that the hypogastrics 

 sometimes contained constrictor fibres for the external gene- 

 rative organs. 



They state that they could discover no satisfactory evidence 

 of the presence of vaso-dilator fibres in any of the upper or 

 lumbar set of nerves. It would appear, therefore, that the 

 vaso-dilator function is probably confined to the lower or 

 sacral set of nerves. 



Following Langley and Anderson's description, the fibres 

 from the sacral set of nerves may be divided into two groups 

 or classes, the visceral and the somatic. Stimulation of the 

 visceral fibres (which run in the nervi erigentes) produces dilator 

 effects on the vessels of the penis (and vulva), as already de- 

 scribed. It also causes inhibition of the unstriated muscles of 

 the penis, the retractor muscle of the penis (when present), and 

 the unstriped muscles of the vulva (in the female). The somatic 

 sacral nerves send motor branches to the ischio-cavernosus and 

 bulbo-cavernosus muscles, as well as to the constrictor urethrse 

 or deeper muscular stratum of the perineum. In the female 

 they innervate the erector clitoridis, which represents the ischio- 

 cavernosus, and the sphincter vaginae, which embraces the 

 lower end of the vagina, and is the homologue of the bulbo- 

 cavernosus. The sacral nerves, as far as Langley and Anderson l 

 were able to determine, send no visceral fibres by their somatic 

 branches. 



The same investigators found that stimulation of the upper 

 or lumbar set of nerves produced strong contraction of the 

 vessels of the penis, 2 as well as contraction of the retractor 

 muscle, and of the other unstriated muscles of the penis, prepuce, 

 and scrotum (dog, cat, and rabbit). The penis underwent 

 marked retraction as a result of the excitation. Stimulation of the 

 2nd lumbar nerves in the cat generally produced a slight but 

 distinct action on the external generative organs. The 3rd, 

 4th, and 5th lumbar nerves in many cases had a strong 

 action, but the 6th had no action. The 1st lumbar and 13th 

 thoracic were found to have a slight action. In the dog stimu- 



1 Langley and Anderson, loc. cit. 



2 Vaso-constrictor fibres for the penis were first found by Eckhard (loc. cit.) 

 in the nervus dorsalis penis. 



