38 INTRODUCTION TO SEXUAL PHYSIOLOGY 



Coition 



The processes involved in seminal ejaculation and penile 

 erection are presided over by one or more (probably two) centres 

 in the posterior or lumbo-sacral part of the spinal cord. The con- 

 dition of tumescence is brought about by stimulation of nerve 

 endings in the penis, of which, as we have seen, it is well provided, 

 and afferent impulses are carried by sensory nerves from this 

 organ to the spinal cord. The stimulation is usually augmented 

 by impulses arising in the brain and induced by the emotions of 

 courtship. Thus the process may be said to be partly physical 

 and partly mental. There is no doubt that the actual friction 

 set up between the male and female sexual organs is largely 

 responsible for the consummation of the process, involving as 

 it does the full functional activity of all the organs in the generative 

 tract. Eckhard and others have shown that the efferent impulses 

 coming from the spinal cord and producing erection, travel along 

 branches of the first, second, and third sacral nerves which are 

 vaso-dilator in function, and if stimulated in a dog by an electric 

 current bring about a state of tumescence. 



Seminal ejaculation is brought about by a series of muscular 

 contractions which begin in the walls of the vasa efferentia 

 and pass to the epididymis and thence along the vas deferens. 

 The muscles of the vesiculse and prostate contract at the same time, 

 and the secretions of all the accessory glands are poured out. 



Langley and Anderson have shown that the efferent nerves 

 supplying these organs arise in the lumbar region, and that 

 their stimulation in the cat and rabbit produces a powerful 

 contraction of the muscles of the vas and related parts. 



The purpose of penile erection is to give the organ sufficient 

 rigidity to make it easy to insert it into the vagina of the female. 

 The friction set up by intromission causes a reflex discharge of 

 motor impulses in the female as well as in the male, and the 

 uterus undergoes a series of peristaltic contractions. Thus in 

 the rabbit Heape has described a rhythmic dipping of the os into 

 the semen in the vagina, which is thereby sucked up into the 

 uterus. In some animals, however, the semen passes directly 

 into the uterus. Prior to the intromission of the penis the 

 vagina becomes flushed and moistened by the mucus which is 

 secreted ; at the same time the clitoris erects and the surrounding 



