THE UROGENITAL SYSTEM 



413 



in the form of a rudimentary epoophoron and paroophoron. The meso- 

 nephric duct in the female becomes the functionless Gartner's duct. 

 The descensus of the ovaries is slight compared with that of the testes. 



With the development of a horizontal longitudinal septum, the 

 cloaca disappears in placental mammals, and two cavities, the urogenital 

 and rectal, take its place. As this change occurs the ureters shift their 

 connexions from the cloaca to the bladder while the ductus deferentes 

 open into the urogenital cavity or urethra. 



Oviduc-t 

 ~~ Uterus - 



Vagi 



na 



Fig. 339. — Four types of uteri occurring in different groups of mammals. A, duplex, 

 the type found in rodents; B, bipartite, the type found in certain carnivores; C, bicor- 

 nate, the type found in most insectivores and prosimians; D. simplex, the type 

 characteristic of the primates. (From Patten's "Embryology of the Pig," after 

 Wiedersheim.) 



In female mammals a tendency of the Muellerian ducts — which 

 parallel the Wolffian ducts and lie medial to them — to fuse in the median 

 line is evident. Beginning with the monotremes the posterior part of 

 the Muellerian ducts fuse into a single uterus, while their anterior portions 

 remain separate as the paired uterine or Fallopian tubes. The monotreme 

 uterus opens into the urogenital sinus. In the higher mammals a vagina 

 for the reception of the penis is differentiated between the uterus and 

 the urogenital sinus. The vagina is therefore seen to be a portion of the 

 united Muellerian ducts. The duplex character of the vagina appears 

 in the marsupials (didelphians) which have two vaginae. In placental 

 mammals, however, the vagina is single. Four stages in the increasing 



