THE MUSCULAR MECHANISMS OF THE 

 GENERATIVE APPARATUS. 



BY ERNEST H. STARLING. 



CONTENTS : Erection, p. 347 Nervous Mechanism, p. 348 Retractor Penis, p. 349 

 Parturition, p. 349 Nervous Mechanism, p. 351. 



THE act of impregnation consists in the introduction of spermatozoa 

 into the female genital tract, where they may come in contact with and 

 fertilise the ovum, which has been discharged from the ovary by a 

 bursting of the Graafian follicle. We have therefore to describe the 

 changes in the generative organs in both sexes, which accompany this 

 act, and the means by which these changes are brought about. 



Erection. The mechanism by which the erection of the penis is 

 brought about is twofold. The most important factor, as was shown 

 by Eckhard l and Loven, 2 is an active dilatation of the vessels of the 

 penis, especially of the medium and smaller sized arteries. This is 

 shown by the fact that, if the penis be cut across, venous blood merely 

 trickles away from the cut surface, whereas, if erection be excited, the 

 now of blood from the cut surface is increased eight to ten times, and 

 the blood becomes bright arterial in colour. That this vaso-dilatation 

 is the most important factor in erection, is shown by the fact that it is 

 possible to excite erection in an animal, in whom the second factor has 

 been abolished by paralysing the muscles by the injection of curare. 



The second factor is the contraction of the ischio-cavernosus or 

 erector penis muscle, certain fibres of which pass over the dorsal vein 

 of the penis, and compress this vessel when they contract. Although 

 this mechanism undoubtedly assists in the production of erection, yet 

 it is unable by itself to cause erection, since ligature of the veins coming 

 from the penis is unable to do so. 



Before or at the beginning of coitus, analogous erectile changes 

 occur in the female organs, leading to erection of the clitoris and of the 

 other erectile structures of the vulva. The friction between the glans 

 and the wall of the vagina causes a reflex discharge of motor impulses 

 in both female and male. In the male, the muscle in the walls of the 

 vasa deferentia and vesiculse seminales enters into peristaltic contrac- 

 tions, thus forcing the contents of these receptacles into the urethra. 

 The semen is pressed along the urethra by rhythmical contractions of 

 the bulbo- and ischio-cavernosi muscles, which empty this canal from 

 behind forwards. At the same time it seems probable that movements 

 take place coincidently in the uterus, consisting in a change in the 



1 Beitr. z. Anat. u. Physiol. (Eckhard), Giessen, 1863, Bd. iii. S. 125. 



2 Arb. a. d. physioL Anst. zu Leipzig, 1866. 



