64 



THE VERTEBRATE OVARY AND ITS RELATIONSHIP TO REPRODUCTION 



OVIDUCT 

 L LO P I AN 



TUBE) 



AT E R AL 

 AL CANAL 



VA6 I N AL 

 E -SAC 



URINARY 



BLADDER 



UR G EN I TAL SINUS 



Fig. 35. Reproductive structures of female opossum shown from the ventral view. Ob- 

 serve that the ovary and infundibular portion of the Fallopian tube lie dorsal to the horn 

 of the uterus. 



functions to secrete an albuminous coating which is applied to the egg during 

 its passage through this region. In amphibians, reptiles, and birds it forms 

 the major portion of the oviduct, but in mammals it is much reduced in size 

 and extent. In the latter group it is referred to as the uterine or Fallopian tube. 



The uterus is a muscular, posterior segment of the oviduct. Like the 

 anterior glandular portion of the oviduct, it also has glandular functions, but 

 these are subservient to its more particular property of expanding into an 

 enlarged compartment where the egg or developing embryo may be retained. 

 The protection and care of the egg or of the embryo during a part or all of 

 its development, is the main function of the uterus in most vertebrates. In the 

 frogs and toads, however, this structure seems to be concerned with a "ripen- 

 ing" process of the egg. Large numbers of eggs are stored in the uterine sac 

 of the frog for a period of time before spawning. 



Various degrees of union between the uterine segments of the two ovi- 

 ducts are found in mammals. In the primates they fuse to form a single 

 uterine compartment with two anterior uterine tubes (fig. 29). In carnivores, 

 there is a caudal body of the uterus with two horns extending forward to 

 unite with the uterine tubes (fig. 36). In the rat and mouse, the uterine seg- 

 ments may be entirely separate, coming together and joining the single vaginal 

 chamber (fig. 37). In the opossum the uterine segments are entirely separated, 

 joining a dual vaginal canal system posteriorly (figs. 34, 35, 114). 



