372 OUTLINES OF CHORDATE DEVELOPMENT 



second section is the uterus, thicker walled than the Fallopian 

 tube, and of greatly varying extent in different Mammals, 

 correlated with the number of young produced at one time, 

 for this is the part of the oviduct occupied by the developing 

 embryos. Lastly is the terminal vagina, which opens directly 

 to the outside in all placental Mammals. 



The vaginal region is practically always a single, median 

 structure, formed by the fusion of the lower ends of the two 



FIG. 143. Diagrammatic representation of the human female reproductive 

 organs. Dorsal (posterior) view. From Quain's Anatomy. The posterior 

 walls of the uterus and vagina have been removed to show their cavities, c, 

 Cervix of uterus; fi, fimbriated opening or ostium of oviduct; h, hydatid; i, 

 wider distal part of oviduct; I, round ligament; II, the broad ligament; lo, liga- 

 ment of ovary; o, ovary (naturally the ovary has an oblique or nearly vertical 

 position); od, oviduct or Fallopian tube; po, parovarium; u, fundus of uterus; 

 v, upper part of vagina. 



oviducts. Different groups of Mammals exhibit various 

 degrees in the extent of the fusion of the uterine sections also. 

 Thus in the Rodents the vaginaB alone are fused, the uteri 

 remaining entirely distinct (uterus duplex), in the Carnivors and 

 most Ungulates the uteri are partly fused, partly free (uterus 

 bicornis), and in the Primates the uteri are completely fused 

 and only the Fallopian tubes remain paired (uterus simplex}. 



2. The Ovum and its Ovarian History 



The ova of the placental Mammals are among the smallest 

 known. When fully formed they are usually 0.1-0.3 mm. in 



