262 THE PHYSIOLOGY OF REPRODUCTION 



whole of the urogenital canal, beyond the apertures of the ducts of 

 Bartholini's glands, is prolonged forward to the extremity of the 

 clitoris and terminates in a similar manner to that of the urethra of 

 the male. In this animal, therefore, the vagina is completely absent, 

 the OS uteri opening directly into the urogenital canal, which' is 

 elongated and tubular in form as in the male. A somewhat similar 

 condition has been known to occur abnormally in the human female.^ 



The Mechanisms of Eeection, Ejaculation, and Eetbaction 



, The erection of the penis is brought about mainly by the dilatation 

 ■oi its blood-vessels. Pirst of all the bulbous (proximal) part of the 

 organ increases in size, and then the swelling extends throughout 

 the cavernous bodies, and eventually to the glans. If the penis is 

 cut across when in a state of relaxation only a small quantity of 

 venous blood exudes from the wound ; but if the same operation is 

 performed during erection, the blood flow is enormously increased, 

 while simultaneously becoming bright and arterial in colour.^ 

 Fran^ois-Franck ^ observed a corresponding rise in the arterial and 

 venous tension. He found also that the organ in the process of 

 erection became very considerably swollen in size before the increase 

 in the blood pressure had extended to the veins. Lov^n* showed 

 that the veins in the penis are traversed by five times as much 

 blood during erection as they are in a state of repose. The same 

 investigator found that, whereas the ordinary arterial pressure in 

 the penis is about half that of the carotid, during erection it rose 

 to three-fifths that of the carotid. The increase in the amount of 

 blood in the organ is accompanied by a rise of temperature.^. 



There can be no doubt that the erection of the penis is brought 

 about partly through the contraction of the ischio-cavernosus (or 

 erector penis) and bulbo-oavernosus muscles, certain of the fibres 

 of which pass over the efferent vessels, and so arrest the outward 

 fiow.of blood.® The result of this contraction is, that whereas the 



' Watson (M.), " The Homology of the Sexual Organs, etc.," Jou7: of Anat. 

 and Phys., vol. xiv., 1879. See also note on p. 272 for other orders. 



^ Eckhard, " Untersuchungen (iber d. Erektion d. Penis beim Hunde," 

 Beitr. zxvr Anat. und Phys., vol. iii., Giessen, 1863. 



^ Erangois-Franck, "Kecherches sur I'lnnervation Vaso-motrice du Pdnis," 

 Arch, de Phys., 1895. 



^ Lov^n, Berichte uher die Verhandlungen der Konigl. Sachs. Oesell. zu Leipzig, 

 vol. viii., 1866. Nikolsky, " Ein Beitrag zur Physiologie der Nervi erigentes," 

 Arch.f. Anat. u. Phys., Phys. Abth., 1879. 



^ Retterer, Article on "Erection," in Eichet's Dictionnaire de Physiologie, 

 vol. v., 1902. 



" De Graaf (Begner), De Vironim Organis Oenerationi Inservientihus, 

 Geneva, 1785. Giinther, Untersuchungen und Erfahrungen aus dem Oebiete 

 der Anatomie, vol. i., Hanover, 1837. Kobelt, De VAppa/reil du Sens Oinital 

 des Deux Sexes, Strasbourg, 1851. For further references, see Eetterer, loc. cit. 



