222 THE FEMALE REPRODUCTIVE SYSTEM 



this instance, however, the male develops a sort of penis, which is 

 inserted for internal copulation. In other mammals there is a 

 urogenital vestibule separated from the anal opening of the digesti\e 

 tract. Into this \'estibule the genital system opens usually by a 

 single passage, the vagina. The upper end of the Miillerian duct 

 functions in conducting the egg to the lower region, or uterus, which 

 is specialized to receive and nourish the developing embryo, and 

 the extreme outer end is modified to receive the copulatory organ 

 of the male for insemination. In some cases the egg-conducting 

 portions, the oviducts or Fallopian tubes, may join a single uterine 

 portion ; in others, the lower portion of each tube has a uterine por- 

 tion and fusion occurs just before the vagina is reached. 



In many mammals, including numerous rodents (mice, rabbits, 

 and beavers), certain bats, and other forms, there is a condition 

 known as uterus duplex, in which there are two separate uteri 

 opening into separate vaginae that fuse near the vestibule. In 

 other mammals, as in certain rodents, some ruminants, and car- 

 nivors, there is a condition known as uterus bi])artitus, in which 

 there is a partial fusion of the two uteri near their junction with 

 the single vagina. x\mong certain other ruminants and carnivors 

 there is a greater posterior fusion of the uterus and an anterior pro- 

 longation to join each Fallopian tube, a condition known as uterus 

 bicornis. x\mong the primates generally, there is a complete fusion 

 of the uterine portions to a single uterus continuing into a single 

 vagina, a condition known as uterus simplex. 



Each oviduct is a relatively short, narrow, convoluted duct, 

 extending from the o^'ary toward the mid-line, where it connects 

 with the anterior lateral face of the uterus. The proximal end 

 broadens out funnel-like and tesselated processes surround the 

 ostium alidominalis. These fiml^riated processes rather closely 

 cover the ovary. The structure of the tube varies somewhat, but 

 three regions can be distinguished throughout. Externally there is 

 an adventitia of connective tissue surfaced with mesothelium. 

 Medially there is a muscularis composed of an external sheath of 

 longitudinally disposed smooth muscle cells and an internal sheath 

 of circular cells. Internally there is a mucosa of ciliated columnar 

 and occasional glandular cells resting upon a timica ])ro])ria of con- 

 nective tissue. No submucosa is distinguished. Near the ostium 

 the nnicosa is elaborately folded, so that sections show a great 

 number of spaces among labyrinthine folds. (I'ig. 1 •>!>.) Toward 

 the uterus these foldings are not so extreme, and the tube wall is 



