MORPHOLOGY OF THE HUMAN URINOGENITAL TRACT. 349 



represent the Wolffian ducts, and that the mesial cul-de-sac is 

 Milllerian. The evidence for this is as follows : — 



' Naked eye. — That the central portion is Mlillerian is quite 

 evident. It has the os uteri of each horn at its upper part;. 

 Owen further figures the remains of a septum in the mesial 

 portion. The lateral canals occupy the position of the per- 

 sistent Wolffian ducts, have the ureter on their inner aspect, 

 and open below into the urinogenital sinus. 



The permanent arrangement in the marsupials is what we 

 find in the hnman embryo at or about the sixth to seventh 

 week of intrauterine life. AVe have, therefore, in the marsupials 

 the primitive developmental condition of the urinogenital 

 ducts remaining, instead of coalescing, as in the higher 

 mammals ; the Milllerian element may be less evident, as in 

 the opossum, or both elements may be well represented, as in 

 the Macropodidse. 



As to tlie function of the lateral canals, it has been ascer- 

 tained that the seminal fluid is transmitted by them, and that 

 the foetus in certain cases passes along them (Hill). According 

 to some authors the foetus passes by the central portion even 

 when this does not open into the urinogenital sinus, and Hill 

 records a case where the foetus did not pass by the lateral canals 

 but into the connective tissue between them, the central pouch 

 being absent. 



Muroscopical. — The microscopical structure varies in the case 

 of the central and lateral canals, the former being lined with a 

 single layer of columnar epithelium, like that of the human 

 cervix nteri, while the latter are lined with many layers of 

 squamous epithelium. This, however, is considered more fully 

 presently. 



An important point is the relation of the nreter to the vagina 

 in the adult female mamn^al, as well as that of the ureter to the 

 urinogenital ducts in the mnmmalian foetus. With the present 

 tendency of biological thought one would e.xpcct these relations 

 to be on a common plan. In the kangaroo adult the ureters 

 pass inside the lateral canal and outside the central vaginal 

 canal before entering the bladder. Their relations are well seen 

 at fig. 27. There one can note the ureters passing down from 

 the kidney to run behind the coi'nua, and, at a lower level, tO' 



