iv THE GENEEATIVE SYSTEM OF THE MALE 151 



But, besides the diffuse excitatory centres of the reflexes of 

 erection and ejaculation, there are in the brain and cord also 

 inhibitory centres for these reflexes. As a proof of this the 

 following fact observed by Goltz is important ; it is much more 

 difficult by manipulation of the prepuce to produce erection and 

 ejaculation in the intact dog than in the dog with the lumbo- 

 sacral portion of the cord separated from the cervico - dorsal, 

 because in the latter case the inhibitory influences emanating 

 from the superior centres are eliminated. If, moreover, in the intact 

 dog one succeeds in obtaining erection in a reflex way, it is easy 

 to make it disappear by electrical stimulation of the skin of a 

 hind-paw, which excites reflexly the supposed cerebral or spinal 

 centres for the inhibition of erection. 



From the fact easily observable that there may be spermatic 

 ejaculation without erection, even in relatively normal conditions 

 of the functions of the genital apparatus, it may be argued that 

 the central nervous organs concerned in ejaculation are distinct 

 anatomically and functionally from those of erection. Ee'iny 

 (1886) found alongside the inferior vena cava a small ganglion, 

 the excitation of which determined only ejaculation. That there 

 exist distinct centrifugal nerves for the two functions is known ; 

 for stimulation of the nerve filaments which supply the vas 

 deferens in rabbits easily arouses expulsive movements, without 

 producing the least erection (M. Loeb, 1866). It is also probable 

 that the centres for the two acts are distinct. If, however, this 

 last proposition is granted, it is necessary to conclude that the 

 two centres are in intimate functional relation with one another, 

 because experience shows that the same peripheral stimuli produce 

 erection when they act with moderate intensity and duration, and 

 ejaculation also when they are stronger and more protracted. 



On the complicated sacral nervous flexus of rabbits, cats, and 

 dogs, numerous and minute researches were made by Langley 

 and Anderson (1895 - 96), with the object of determining by 

 physiological methods the innervation of the genital organs. In 

 man the nervous supply is probably similar to that of the dog. 



The nervus erigens contains spinal fibres proceeding from the 

 first and second sacral roots, and sympathetic fibres proceeding from 

 the hypogastric plexus and the mesenteric plexus. From these 

 sympathetic fibres emanate the nervous filaments which supply 

 the corpora cavernosa. 



The nervus pudendus arises by four branches proceeding from the 

 first four sacral roots. The perineal branch is the motor nerve of 

 the ejaculatory muscles ; the dorsal branch of the penis is the sensory 

 nerve of the greatest part of this organ. To the pudendal nerve 

 also pass sympathetic fibres from the hypogastric plexus. 



The nervus erigens, as well as the nervus pudendus, contains 

 numerous vaso -constrictor and vaso-dilator fibres ; the first are 



