184 ELEMENTS OF MAMMALIAN ANATOMY. 



REMARKS ON THE MAMMALIAN URO GENITAL 



SYSTEM. 



The urogenital system is subject to some variations in 

 the different orders of Mammalia. In the Ornithodelphia, 

 the mammary glands are devoid of teats and the oviducts 

 corresponding to the Fallopian tubes and horns of the 

 uterus do not unite in the median line to form the body 

 of the uterus, but unite with the urethra, forming the 

 urogenital canal. The latter opens into an enlarged 

 terminal portion of the rectum, called the cloaca. The 

 ureters also open directly into the cloaca, so that there 

 is but one external opening for the genital and excretory 

 products. In the above features the Monotremes resem- 

 ble the Amphibia and reptiles. All mammals are vivip- 

 arous except the Monotremata, which are oviparous, 

 laying eggs as large as those of the robin. The Orni- 

 thorhynchus incubates its eggs in an underground nest, 

 while the Echidna carries hers in a temporary abdominal 

 pouch. 



The Marsupialia bring forth their young in a very 

 immature condition. They are then carried for several 

 months in an abdominal integumentary pouch, the 

 marsupium, within which are the nipples. In the Mono- 

 tremata, Cetacea, Sirenia, and elephant the testes do not 

 descend into a scrotum, but are retained in the primitive 

 location within the abdomen. In Primates and some 

 Edentates, the uterus is merely a pear-shaped body 

 without any cornua, the Fallopian tubes leading directly 

 into the body of the uterus. 



In the ox, bears, seals, and cetaceans the kidneys are 

 distinctly lobulated. Internal evidence of lobulation is 

 presented in most mammals by the renal papillae. In the 

 embryo the kidneys of all mammals are lobulated. 



