THE ACCESSORY REPRODUCTIVE ORGANS 261 



cut off the ram is rendered barren. Professor Robert Wallace 

 informs me that it used to be a regular practice, for the protection of 

 ewes while being driven south from the Highlands of Scotland, to cut 

 off the filiform appendage from the rams to prevent them from 

 impregnating the ewes on the way, this method of inducing sterility 

 proving quite as effective as removal of the testicles. 



In the bull, the musk ox, and some other Ruminants the filiform 

 process is vestigial. The end of the penis itself (the glans) is some- 

 what pointed in the bulb and it is believed that it is inserted into the 

 os uteri in copulation. It does not swell up to the same extent as 

 in the stallion, where the erected organ almost fills the vagina of 

 the mare and much friction takes place before ejaculation is com- 

 pleted. The urethral aperture is central in the horse, as in the boar. 



In the dog the process of coition is very prolonged. This is due 

 to the contraction of a sphincter in the female which prevents the 

 withdrawal of the male organ until almost fully relaxed. 1 



FIG. 73. Distal end of bull's penis as seen from left side, showing glans and 

 urethral papilla representing vestigial filiform appendage. The prepuce 

 is folded back. About two-thirds natural size. 



The penis in the male mammal is represented in the female by 

 the diminutive clitoris. This organ, however, is not traversed "by the 

 urethra (at least in the majority of animals). On the other hand, 

 the corpora cavernosa and the glans are represented by homologous 

 structures. The clitoris, like the penis, contains very numerous sensory 

 nerve endings 2 and undergoes erection during sexual congress. 



The relation between the clitoris and the urogenital canal is 

 closer in some Mammals than in others. In some species (e.g. the 

 capybara among the Rodents, and Tupaia among Insectivores) the 

 clitoris is of considerable size, and is grooved along its under surface 

 in relation to the upper wall of the urethra. In other animals (e.g. 

 Ai'vicola, Talpa, and Stenops) the groove on the under surface of the 

 elongated clitoris is converted by the coalescence of its margins into 

 a tube, which constitutes the urethral portion of the urogenital 

 canal. Further, in the female of the spotted hyena (If. crocuta), the 



1 Prolonged retention has also been known to occur with the human subject. 



2 Worthmann, " Beitrage zur Kenntniss der Nervenausbreitung in Clitoris 

 und Vagina," Arch. f. Mikr. Anat., vol. Ixviii. 



