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LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



ft) Female: The ovaries are masses of connective tissue containing the developing eggs, 

 each egg surrounded by a capsule of nutritive cells forming a follicle. The ovaries, unlike the 

 testes, never have any connection with the kidneys. The ducts of the ovaries are named the 

 oviducts or Mullerian ducts. The origin of the Miillerian ducts is somewhat problematical. 

 In elasmobranchs they arise by a splitting of the pronephric duct; half of the pronephric 

 duct then becomes the oviduct, and the other half becomes the mesonephric duct. Al- 

 though this mode of origin is the one commonly accepted, it cannot be demonstrated for 

 other vertebrates; in them the oviducts arise independently in the mesomere. The oviducts 

 are never directly connected with the ovaries. They open into the coelom near the ovaries 



uterine tube 



oviduct 



cloaca 



rethra 



uterine tube 



urogenital sinus 



uterine tube 



uterus 



uterine tube 



urethra"'! 

 urogenital sinus 



FIG. 63. Diagrams to show the various types of mammalian oviducts. A, condition found in 

 the majority of female vertebrates; the two oviducts are completely separate and open independently 

 into the cloaca. B-E, various conditions found in mammals, showing differentiation of the oviducts 

 into uterine tube, uterus, and vagina, and progressive fusion of the lower parts of the oviducts: B, duplex 

 type found in rodents, in which the two vaginae are united to one; C, bipartite type occurring in carni- 

 vores; not only are the vaginae fused but the lower parts of the two uteri are fused to form a single 

 body, divided in two by a partition which represents the fused walls of the two uteri; the upper parts of 

 the two uteri remain separate as the horns; D, bicornuate type, found in many ungulates, similar to C 

 except that the partition has disappeared; E, simplex type, occurring in man and the apes, in which 

 both vaginae and uteri are fused along their entire lengths leaving only the uterine tubes separate. 

 Note further that in B-D the urethra joins the vagina to form the urogenital sinus which opens to 

 the exterior, while in E the urethra and vagina are wholly separate and open independently to the 

 exterior. (From Wiedersheim's Comparative Anatomy of Vertebrates, courtesy of the Macmillan 

 Company.) 



by a funnel-shaped opening, the ostium, which probably represents one or more of the nephro- 

 stomes of the pronephros (Fig. 62!$ and D). The eggs escape from the ovary by rupture of 

 the ovarian wall, pass into the ostium of the oviducts by methods which are not always under- 

 stood, and are conveyed down the oviducts. 



The oviducts in the majority of vertebrates remain as two separate tubes opening into 

 the cloaca (Fig. 63^!). In mammals each oviduct is differentiated into a narrower anterior 

 portion called the uterine or Fallopian tube, which bears the ostium, and a wider more muscular 

 posterior portion, the uterus. In the monotremes, or egg-laying mammals, each uterus opens 

 separately into the cloaca. In the marsupials the terminal portion of the uterus is differentiated 



