UROGENITAL SYSTEM. 339 
In the placental mammals the posterior (vaginal) ends of the two 
Miillerian ducts fuse in the median line, thus forming a single vagina. 
In some the two uteri remain distinct, each having its own opening 
(os uteri) into the vagina. This forms the uterus duplex (figs. 339, B, 
340, II), found in most rodents. In carnivores, ruminants, horse and 
Fic. 338.—Female genitalia of Echidna, after Owen. a, openings of ureters into, 
ug, urogenital sinus; 6, bladder, a bristle passing into urogenital sinus; c, cloaca; d, opening 
of rectum into cloaca; 0, ovary, od, oviduct, the lower part uterine, 7, rectum; u, ureters. 
pig the fusion has been carried farther so that there is.a single os uteri 
and the two uteri are almost completely separated (uterus bipartitus, 
fig. 340, ZZ) or the fusion is carried farther, the result being the 
uterus bicornis (fig. 339, C) in which the double nature is still shown 
by the two pouches at the upper (anterior) end. Lastly, in the pri- 
mates, the fusion of the two primitive uteri is complete, the result 
being the uterus simplex (figs. 339, D; 340, IJJ-VI), in which the 
