UROGENITAL ORGANS 377 



some analogous structure in the ovary governing the development of female 

 characteristics and controlling some of the features of menstruation. 



There are a number of accessory glands connected with the genital ducts, 

 these being usually better developed in the male than in the female. Only the 

 more prominent are mentioned here. The seminal vesicles (present in some 

 rodents, bats, insectivores and in ungulates and primates) are a pair of tubular 

 or saccular glands opening into the vasa deferentia just before their entrance 

 into the urogenital canal. The prostate glands, which occur in all placental 

 mammals with the exceptions of edentates and whales, are connected with the 

 urogenital canal. Farther along the canal are Cowper's glands which occur in 

 almost all mammals as scattered bodies or aggregated into larger masses, and 

 surrounded by smooth muscle. 



Concerning the functions of these glands considerable uncertainty exists. 

 From the fact that removal of the prostate and the seminal vesicle in rats pre- 

 vents fertilization, and the further fact that the secretion of the seminal 

 vesicles increases the activity of the spermatozoa, it seems probable that they 



Fig. 401. — Diagram of male genitalia of beaver, Castor canadensis, after Weber. 

 a, anus; ag, anal gland; b, urinary bladder; gv, gland of vas deferens; oa, opening of anal 

 gland; op, os penis; p, prostate; pp, preputial gland; r, rectum; u, ureter; vd, vas deferens. 



are of great importance in connexion with fertilization. Then it has been shown 

 that in some instances the coagulation of the secretion of these glands closes the 

 vagina after copulation has occurred, thus preventing the exit of the sperm. 



In the monotremes the urogenital sinus empties into the cloaca, 

 from which waste from the digestive canal as well as urinary and 

 reproductive products pass to the exterior through a single opening 

 (whence the name monotreme). In all other mammals there is a 

 more or less complete separation of faecal and urogenital matter. This 

 is accomplished by a horizontal partition which divides the cloaca 

 into a dorsal rectum and a ventral urogenital portion, the wall be- 

 tween them being the perineum. This is but slightly developed and 

 not appearing from the exterior in marsupials, where there is an 

 inpushing of the external skin so that only one opening is visible. 

 The same is true in a less degree in rodents (lig. 401) and insectivores. 



