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EMBRYOLOGY 



tended by an enlargement of the arterioles of supply, and that there is 

 not simply a stasis of blood produced by constriction of the veins, ex- 

 cept possibly for a short time during the period of greatest excitement. 

 In experiments on dogs, Eckhard found a nerve derived from the sacral 

 plexus, stimulation of which produced an increase in the flow of blood 

 through the penis, attended with all the phenomena of erection. This 

 nerve arises by two roots at the sacral plexus, from the first to the third 

 conte sacral nerves, and is connected with the genito-spinal centre in the 

 lower part of the lumbar region of the spinal cord. In the experiments 

 referred to, by a comparison of the quantity of venous blood coming 

 from the penis before and during the stimulation of the nerve, Eckhard 

 found a great increase during erection. It is probable that in addition 

 to the arterial dilatation, when the penis attains its maximum of rigidity, 

 there is a certain degree of obstruction to the outflow of blood by com- 

 pression of the veins, and thatrthe rigidity is increased by contraction of 

 the trabecular muscular fibres of the corpora cavernosa. At the climax 

 of an orgasm, the semen is forcibly discharged from the urethra by 

 spasmodic contractions of the vesiculae seminales and the ejaculatory 

 muscles. Although this is the physiological mechanism of a seminal 

 discharge, friction of the parts, which usually precedes ejaculation, is 

 not absolutely necessary, as is shown by the occurrence of orgasm dur- 

 ing sleep, which is likely to take place in healthy men after prolonged 

 continence. 



There are some females in whom the generative function is per- 

 formed, even to the extent of bearing children, who have no actual 

 knowledge of a true venereal orgasm ; but there are others who experi- 

 ence an orgasm fully as intense as that which accompanies ejaculation 

 in the male. There is, therefore, the important difference in the sexes, 

 that preliminary excitement and an orgasm are necessary to the perform- 

 ance of the generative act in the male but are not essential in the 

 female. Still, there can be scarcely a doubt that venereal excitement 

 in the female facilitates conception, other conditions being favorable. 

 When excitement occurs in the female, there is engorgement of the true 

 erectile tissues and possibly of the convoluted vessels surrounding the 

 internal organs. The neck of the uterus becomes hardened and slightly 

 elongated ; and it has been observed by Litzmann and others, that there 

 occurs a sudden opening and closing of the os, which exerts more or 

 less suction force. These conditions, however, are not essential to fe- 

 cundation, although they may exert a favorable influence on the pene- 

 tration of spermatozoids and may at certain times determine the rupture 

 of a Graafian follicle. 



The spermatozoids, once within the cervix uteri, and in contact with 



