374 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



monotremes (figs. 398, $gg,A, 4oo,/),ananteriorFallopiantubeanda 

 more posterior uterus, the lines between the two not being sharply 

 drawn. The Fallopian tube connects with the coelom by a broad 

 and fringed ostium, while the tube itself secretes the albumen which 

 surrounds the eggs. The uterus is more muscular and its walls form 

 the horny shell (with calcareous deposits in the duckbill) around the 



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Fig. 398. — Female genitalia of Echidna, after Owen, a, openings of ureters into, 

 ug, urogenital sinus; b, bladder, a bristle passing into urogenital sinus; c, cloaca; d, 

 opening of rectum into cloaca; 0, ovary; od, oviduct, the lower part uterine, r, rectum; 

 u, ureters. 



egg. Distally each uterus opens directly into the urogenital sinus 

 which connects with the cloaca and so with the exterior (fig. 398). 



In all other mammals the lower end of theMiillerian duct, between 

 the uterus and the urogenital sinus, is differentiated as a vagina 

 to receive the copulatory organ of the male. In the marsupial there 

 are two vaginae, and in some the vaginae of the two sides fuse near the 

 uterus so that a caecal pocket results (fig. 399, B), and in a few this 



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