( B8 ) 



and, conliiiuuig their course again in a cranial direction, pierce 

 tiic posterior wall of the bladder in an oblique, caudo-cranial direction 

 and open into this organ on two adjacent papillae with ostia, which 

 are turned towards the fundus of the bladder. It is verv remarkable 

 that the course of the ureters at this stage already agrees completely 

 with the adult condition. The question as to the cause of the hook- 

 shaped bend in the ureters of marsupials, which has already long been 

 known, and which, in my opinion, must exactly be sought in the 

 above-mentioned bridge between the two genital cords, will be 

 briefly discussed later on. 



With regard to the mutual relation of the WolfHian and MüUorian 

 ducts, we hav^e to offer the following remarks. At the level of the 

 caudal pole of the primitive kidney, the Miillei-ian duct lies ventrally 

 and a little laterally of the Wolffian. In a caudal direction this 

 relation is changed, the MiiUerian duct being gradually shifted towards 

 the ventro-mcdial side of the Wolffian duct. This topograpliical 

 relation exists until near the place where they enter the uro-genital 

 sinus. In their course they follow the genital cords and, in doing so, 

 bend medially, then caudo-laterally and finally, in the last part of 

 Iheir course, show very peculiar cliaracteristics. 



The MiiUerian duct snddeidy bends venlrally and medially, 

 describes a caudally slighlly convex arc and (hen opens into the 

 uro-genital sinus. 



The Wolffian duct, at first situated dorso-laterally of that of 

 Muller, describes like this latter in its terminal portion a caudally 

 convex arc and so becomes placed caudally of the MiiUerian duct. 

 Next it bends medially aiul lays itself against the medial wall of 

 the MiiUerian duct, after which it opens into the uro-genital sinus, 

 cranially of the latter. 



Hence it appears that the Wolffian duct in the last pai't of its 

 course describes almost a complete spiral revolution round the MiiUerian 

 being successively dorso-lateral, caudal (dorsal), medial and cranial. 

 This course I have schematically represented in figure 2, seen from 

 the front and somewhat from above. The bladder has in the figure 

 been imagined cut off exactly at the level where the Wolffian 

 duct enters. 



F. Keibel ^) has suggested that in marsupials the ureters enter 

 into communication with the bladder already at the stage in which 

 they appear as sprouts of the dorso-medial wall of the Wolffian 



1) F. Keibel. Zur Entwicklungsgeschichte des menschlichen Uro-geniialnpparafes 

 Archiv liir Anatomie und Entwicklungsgeschiclite. ISOG. p. 55. 



