NERVE SUPPLY OF SKIN OF GENERATIVE ORGANS. 635 



end in the ganglion stellatuin, from which the post-ganglionic fibres are 

 given off to the brachial nerves. The origin of these fibres closely 

 resembles that of the pilo-motor fibres (cf. table), with the exception 

 that the ninth thoracic nerve, whilst sending secretory and vasomotor 

 fibres to the ganglion stellatuin, does not send pilo-motor fibres to it. 

 The maximum effect is usually obtained with the seventh nerve, the 

 nerves above and below giving progressively less effect. 



Occasionally there is slight secretion and pallor in the fore-foot on 

 stimulating the third thoracic, possibly also from the tenth. Bayliss and 

 Bradford found, in the dog, that the tenth and sometimes the eleventh nerve 

 caused vaso-constriction in the fore-limb, and that the eleventh to the third 

 lumbar caused vaso-constriction in the hind-limb. 



4. The vasomotor fibres for the tail have very nearly the same 

 origin and connections as the pilo-motor fibres for this region. They 

 appear, however, to be a little more posterior. 



General differences accompanying a posterior plexus. — With a 



posterior arrangement of nerves, the fourth lumbar nerve in the cat sends fibres 

 to the coccygeal ganglion, and, according to the degree of downward shift, to 

 more and more of the ganglia above up to the fifth lumbar. The posterior 

 arrangement also considerably affects the connection of the seventh to the 

 eleventh thoracic nerves. Of these nerves, four always send some fibres 

 up and some down in the sympathetic chain ; the remaining one, the eleventh 

 thoracic nerve, may or may not do so. For details with regard to the 

 variations in ganglionic connection of these nerves, the original papers must be 

 referred to. The connection of the other nerves — except, perhaps, the third 

 lumbar — are comparatively little affected by a shifting in their origin. 



Sympathetic Nervous Supply of the Skin of the External 

 Generative Organs and of the Ano-Genital Eegion. 1 



Effects produced by stimulation. — Stimulation of the lumbar 

 sympathetic chain causes contraction of the unstriated muscles and 

 blood vessels of the skin of the ano-genital region, and of the penis or 

 vagina. The degree of contraction varies considerably in different parts 

 and in different animals. We may mention the effects in the cat, dog, 

 and rabbit in the male. In the female the effects are mutatis mutandis 

 the same as in the male, but most of them are much less marked. 



In all three animals the lumbar sympathetic causes strong contraction 

 of the blood vessels, of the unstriated muscles of the body of the penis 

 and of the prepuce, and of the retractor muscle of the penis. The 

 retractor muscle is well developed in the dog, and, as in some other 

 animals, it is a thin band of longitudinally arranged unstriated muscle, 

 inserted at the attachment of the prepuce, and continued backwards in 

 the middle line over the ventral surface of the corpus spongiosum and 

 bulbus urethrse. In the cat and dog there is strong contraction of the 

 tunica dartos of the scrotum ; but the blood vessels of the scrotum are 

 not strongly affected. In the rabbit the scrotal contraction is very 

 slight. In the cat and dog there is little movement of the skin of the 

 ano-genital region, apart from that of the scrotum. Tn the rabbit the 

 skin covering the body of the penis contracts strongly. 



1 For list of papers and more detailed account, cf. Langley and Anderson, Journ. 

 Physiol., Cambridge and London, 1895, vol. xx. p. 85. 



