IV. VERTEBRATA: MAMMALIA 



557 



openings into the body cavity (/) and the uterus (). The ureters open 

 into the sinus between the uterine openings. In the marsupials (B and C) 

 there are three divisions, oviduct, uterus, and vagina; besides, the two 

 Miillerian ducts may approach, near the uterus (B), or fuse in this region 

 (C) in some species, forming an unpaired blind sac (vb), which may even 



9" 



*A'i' 



FIG. 604. Female genitalia of (.4) Echidna aculeata; (B) of Didelphys dorsigera; 

 (C) Phascolomys -wombat (B and C, after Wiedersheim). d, cloaca; d, rectum; 

 h, urinary bladder; n, kidney; o, ovary; od, oviduct; pu, mouth of ureters; su, urogenital 

 sinus; t, ostium abdominale tubs; u, uterus; u', opening into vagina; ur, ureter; v, 

 vagina; vb, vaginal blind sac. 



open into the urogenital sinus as a third vagina. This partial fusion of 

 the vaginae of the marsupials is completed in the placental mammals, the 

 single vagina and the sinus forming a single canal (rig. 605). Here the 

 uterine portions may remain distinct (uterus duplex or rodents, A), or they 

 may fuse partially (uterus bicornis of insectivores, whales, ungulates, and 



FIG. 605. .4, uterus duplex; B, uterus bicornis; C, uterus simplex (from Gegen- 

 baur). od, oviduct; u, uterus; v, vagina. 



carnivores, B}, or they may be completely fused (uterus simplex of apes 

 and man, C). 



Thus there are three different types of the female genitalia, in which 

 the vagina is not differentiated (Ornithodelphia), or is double (Marsupi- 

 alia), or is single and unpaired (Monodelphia). To these correspond 

 three types of development. The Ornithodelphia are oviparous, the 



