1128 THE REPRODUCTIVE ORGANS 



toward a more abundant content in blood at any one time. This con- 

 clusion is strengthened by the fact that in priapismus this organ may 

 retain its erected condition for hours and even for days without show- 

 ing an actual impairment of its tissues or gangrene. Naturally, the 

 size and shape of the erected organ are determined not only by the dis- 

 tention of the cavernous spaces, but also by the arrangement of its gross 

 anatomical structures, such as its dorsal fascia and the fascia situated 

 in the vicinity of its base. The former acts in the manner of a ligament. 

 Since it is shorter than the one investing the under surface of this 

 organ, the dorsal aspect of the erected penis must exhibit a decided 

 concavity. This change in its shape imparts to it a greater penetrating 

 power and increases its receptive power to stimuli, because it tends to 

 retract the prepuce and to uncover the tactile receptors of the glans 

 penis. During this period it is quite impossible to void urine, because 

 the sphincter vesicae remains firmly closed. Not until the erection 

 has ceased does this sphincter regain its power of relaxation.^ 



The reflex center controlling this act is situated in the lumbar 

 segment of the spinal cord. The corresponding autonomic fibers 

 leave this structure in the first to third sacral nerves to form the pelvic 

 plexus and nervi erigentes and cavernosi. The fact that the latter 

 contain vaso-dilator fibers to- the penis has been proved by Eckhard, 

 Loven and others by stimulating them electrically. Afferently, this 

 reflex center may be activated by stimuli applied to the genitals 

 directly, as well as by stimuli received from other sense-organs and the 

 cortical association centers. 



The Act of Ejaculation. — The discharge of the semen is initiated 

 by a powerful peristalsis of the vas deferens, seminal vesicles and 

 ejaculatory duct which forces the secretion into the urethra. Here it 

 is prevented from entering the deeper urethra by the sphincter vesicae^ 

 and is mixed with the secretions of the prostate and Cowper's glands. 

 The latter are poured into the urethra in the hollow at each side of 

 the colliculus seminalis. Then begin the rhythmic contractions of 

 certain striated muscles which, however, are not under the control 

 of the will. Chiefly involved in this process are the ischio-cavernosus, 

 the bulbo-cavernosus and the sphincter urethrse membranacese or 

 sphincter of Henle. 



The act of ejaculation is controlled by a reflex center which is 

 situated in the lumbar segment of the spinal cord. The latter may be 

 activated by afferent stimuli arising in the genital organs and evoked 

 chiefly in Krause's corpuscles with which the glans penis is abundantly 

 supplied. Other sense-organs, such as the general cutaneous receptors, 

 the retina, and organ of Corti may also be involved, but only in so far 

 as their impressions give rise to erotic associations. In the absence 

 of peripheral stimuU, the activation of the psychic centers may lead to 

 ^'spontaneous" emissions, those occurring in consequence of dreams 



1 Zeiss! 8,nd Holzknecht, Wiener med. Blatter, 1902. 



2 Walker, Archiv fur Anatomie, 1899. 



