644 ON THE UBOGEXITAL ORGANS OF THE KAXGAEOO, 



but the height and breadth gradually diminish as the ridge is 

 traced backwards, The median ridge extends backwards for an 

 inch, rapidly decreasing in height posterior to the ostium urethrse. 

 The secondar}' ridges are as long, but at the same time lower and 

 narrower than the main ones. 



These ridges are permanent structures and are not due merely 

 to the contraction of the walls of the canal. Whether they have 

 any functional importance beyond increasing the surface of the 

 mucous membrane lining the urogenital passage, or whether they 

 are in some way connected with the mode of development of this 

 portion of the urogenital organs, is not at all clear at present ; 

 but they form too conspicuous a feature to be passed over in 

 silence. They seem to be absent sometimes in specimens of M. 

 major, though twentj^-five of mine shew them very well. ^STeither 

 Home nor Owen seems to refer to them, though Home's]figures, 

 which however are very poor, give one the idea that there were 

 ridges present, and Prof. Owen speaking of the Wombat says 

 " the urogenital canal is lined by a thick epithelium, and its 

 surface is broken up into countless oblii^ue rug[e and coarse 

 papillse betraying a certain regularity in their arrangement." 



In the median vagina no longitudinal septum was seen, but its 

 ventral surface presents two ridges with a well marked groove 

 between them. They start from the anterior end of the chamber 

 and at f in. from the ostium of the direct communication thev 

 curve outwards and fuse with the side walls. They increase 

 gradually in height from before backwards and the groove 

 separating them averages iV in. in width. When the ridges join 

 the sides the groove opens out into a chamber wh""h opens into 

 the urogenital canal by the direct communication. The ventral 

 wall of this chamber is marked by a slight median elevation. 

 Specimens («) and (h) of my former paper have been referred to 

 for comj^arison, but neither of them presents a similar arrange- 

 ment of ridges and groove. Beyond some slight longitudinal 



