EJACULATION AND RECEPTION OF THE SEMEN. 859 



perinei is perforated by the venae profundse penis, which come from the corpora 

 cavernosa, so that when it contracts it must compress these veins between the 

 tense horizontal fibres (fig. 654, 6). The deep veins of the penis join the common 

 pudendal vein and the plexus Santorini. (3) Lastly, the bulbo-cavemosus is con- 

 cerned in the hardening of the urethral corpus spongiosum, as it compresses the 

 bulb of the urethra (figs. 654, 5, 172). All these muscles are partly under the 

 control of the will, whereby the erection may be increased. Normally, however, 

 their contraction is excited reflexly by stimulation of the sensory nerves of the 

 penis ( 362, 4). 



The congestion of blood is not complete, else, in pathological cases, continuous erection, as 

 in satyriasis, would give rise to gangrene. The accumulation of the blood in the penis is 

 favoured by the fact that the origins of the veins of the penis lie in the corpus cavernosum, 

 which, when it enlarges, must compress them. There are also trabecular smooth muscular 

 fibres, which compress the large venous plexus of Santorini. 



That erection is a complex motor act depending on the nervous system, is proved by an 

 experiment of Hausmann, who found that section of the nerves of the penis prevented erection 

 in a stallion. The imperfect erection which occurs in the female is confined to the corpora 

 cavernosa clitoridis and the bulbi vestibuli. During erection, the passage from the urethra to 

 the bladder is closed, partly by the swelling of the caput gallinagiuis, and partly by the action 

 of the sphincter urethrse, which is connected with the deep transversus perinei. 



437. EJACULATION RECEPTION OF THE SEMEN. In connection 

 with the ejaculation of the seminal fluid, we must distinguish two different factors 

 (1) its passage from the testicles to the vesicuke seminales ; (2) the act of 

 ejaculation itself. The former is caused by the newly secreted fluid forcing on that 

 in front of it, by the action of the ciliated epithelium (which lines the epididymis 

 to the beginning of the vas deferens), and also by the peristaltic movements of the 

 smooth muscular fibres of the vas deferens. Ejaculation, however, requires strong 

 peristaltic contractions of the vasa deferentia and the vesiculae seminales, which are 

 brought about by the reflex stimulation of the ejaculation centre in the spinal cord 

 ( 362, 5). As soon as the seminal fluid reaches the urethra, there is a rhythmical 

 contraction of the bulbo-cavemosus muscle (produced by the mechanical dilatation 

 of the urethra), whereby the fluid is forcibly ejected from the urethra. Both vasa 

 deferentia and vesiculse do not always eject their contents into the urethra simul- 

 taneously. With moderate excitement the contents of only one may be dis- 

 charged. The ischio-cavernosus and deep transversus perinei contract at the same 

 time as the bulbo-cavernosus, although the former have no effect on the act of 

 ejaculation. In the female also, under normal circumstances, at the height of the 

 sexual excitement there is a reflex movement corresponding to ejaculation. It con- 

 sists of a movement analogous to that in man. At first there is a reflex peristaltic 

 movement of the Fallopian tube and uterus, proceeding from the end of the tube 

 towards the vagina, and produced reflexly by the stimulation of the genital nerves. 

 Dembo observed that stimulation of the anterior upper wall of the vagina in 

 animals caused a gradual contraction of the uterus. By this movement, correspond- 

 ing to that of the vasa deferentia in man, a certain amount of the mucus normally 

 lining the uterus is forced into the vagina. 



This is followed by the rhythmical contraction of the sphincter cunni (analogous 

 to the bulbo-cavernosus), also of the ischio-cavernosus, and deep transversus perinei. 

 The uterus is erected by the powerful contraction of its muscular fibres and round 

 ligaments, while at the same time it descends towards the vagina, its cavity is more 

 and more diminished, and its mucous contents are forced out. When the uterus 

 relaxes after the stage of excitement, it aspirates into its cavity the seminal fluid 

 injected into the vestibule (Aristotle, Bischoff). 



But the suction of the greatly excited uterus is not necessary for the reception of the semen 

 {Aristotle). The spermatozoa may wriggle by their own movements from the vagina into the 

 orifice of the uterus [Kristeller). The cases of pregnancy where from some pathological causes 



