The Urinogenital System. 



97 



position. Its gubernacular connections are, however, plainly 

 discernible in the adult animal by the ovarian and round liga- 

 ments, the latter being inserted into a small pocket of the abdom- 

 inal wall simulating the testis sac. 



Though inconspicuous in gross size as compared with the testis, 

 the ovary is concerned with the formation of cells of relatively large 

 dimensions, the female germ cells or ova. These undergo their 

 •PtTTi riTZATjTj- principal development as single cells in the 



AND OVIDUCTS. tissue oi the organ, but at times, through 



rupture of the enclosing follicles, they gain 

 access to the surface, and thence pass directly into the open mouth 

 of the uterine tube. If fertilized; they begin their segmentation 

 and further development into an embryo, the latter becoming 

 attached to the wall of the 

 Uterus. A placental con- 

 nection is formed by which 

 nourishment is carried to the 

 embryo, during the period of 

 intra-uterine life, in the rabbit 

 about thirty days. There are 

 two complete uteri, the cavi- 

 ties of which are connected 



distally with the unpaired vagina, and through this with the 

 urinogenital sinus. The size and appearance of the uteri depend 

 upon the age of the animals examined, and upon whether or not 

 they are pregnant or have borne young. The uteri of pregnant 

 females are greatly enlarged and vascular. They contain from five 

 to eight young, the position of which may be easily seen from the 

 expansion of those parts of the tubes in which they lie. 



The paired condition of the Uteri in the rabbit is especially 

 instructive because of its primitive nature as compared with that 

 in many other mammals. Paired OViductS (Fig. 49A) are the rule 

 in lower vertebrates, where the function is simply to carry the 

 eggs to the outside of the body. This condition is retained with 

 minor modifications to the mototreme stage of mammals, but in 

 higher forms of the latter the ducts are successively coalesced. 

 In marsupials there are still paired vaginae, while in placentals the 

 structure is unpaired. In the rabbit, as in many lower placentals, 



Fig. 54, Three stages of specialization of the 

 A, uterus duplex; B, uterus bicornis; C, 

 uterus simplex, t, uterine tube; u, uterus; v, 

 vagina. 



uterus. 



