UROGENITAL SYSTEM 143 



generally oval in form, lying close to the vertebral column, and 

 the epididymis with the vasa efferentia and vasa deferentia 

 opening into the cloaca. The ovaries are aciniform ; the ovi- 

 ducts (appearing as Miillerian ducts developed from the original 

 Wolffian ducts) form as a rule important passages, each furnished 

 with an abdominal infundibulum and a short excretory duct 

 opening into the cloaca. 



The conditions prevailing among the birds are very similar, 

 with the peculiarity that (with the exception of a few birds of 

 prey) both the ovary and oviduct on the right side are un- 

 developed. This peculiarity occurs also in the Monotremata. 

 Each of the two Miillerian ducts forms a canal (oviduct), which 

 opens into a sinus urogenitalis communicating with the cloaca 

 and forms a uterus at its lower end. 



In the Marsupials the two Miillerian ducts are so connected 

 that on each side a uterus, oviduct and vagina are formed, or 

 the lumina unite into one cavity, whence they again separate to 

 reach the sinus urogenitalis. The Monotremata and Marsupials 

 are mammalia aplacentalia. 



In the Placentalia, to which homo sapiens also belongs, the 

 embryo communicates with the vascular system of the mother 

 through the placenta and remains enclosed in the uterus until 

 fully developed. The germinal glands transformed into 

 testicles are situated at first, like the ovaries, at the inner margin 

 of the Wolffian bodies. When the Wolffian body unites with 

 the testicle the former develops into the epididymis, the Wolf- 

 fian ducts into the vasa deferentia and the Mullerian ducts 

 remain rudimentary. 



Thus, only in the Monotremata do the testicles retain their 

 original position ; in the Cetaceans, Hyrax, elephant and certain 

 of the Edentata the testicles are placed below the kidneys ; in 

 many rodents, the camel and certain of the Carnivora, they 

 occur in the inguinal region of the abdominal wall ; lastly, in 

 many of the mammals and in man they are contained in a 

 scrotum. 



Other conditions obtain among the female members of the 

 mammalia placentalia. The Wolffian ducts do not develop, 

 while the Mullerian ducts form the oviducts, the uterus and 

 vagina. Signs of an earlier structure are seen in the bicornuate 



