ME KIDNEYS. 



169 



manent kidneys, of tubuli uriniferi commencing in dilata- 

 tions; they exercise their functions for a limited period, and 

 then disappear nearly altogether; but their ducts, and other 

 tissue connected with them, are closely associated with the 

 development of the ducts of the essential reproductive organs 

 in both sexes. In reptiles and birds the kidneys have a frilled 

 or convoluted appearance; in mammals they are more com- 

 pact than in any other vertebrata. 



Fig. 88. WOLFFIAN BODIES OF 

 EMBRYO PIG. a, kidney; b, 

 Wolffian body, and, on its sur- 

 face, the Miillerian duct, after- Fig. 89. KIDNEY OF KANGAROO, 

 wards the Fallopian tube ; c, vertical section. a, Ureter ; 

 ovary ; d, urinary bladder b, cone, to the summit of 

 turned down ; e, rectum. which all the tubules are 

 Double size. gathered. 



In the part of their course nearest the circumference of 

 the organ, the tubules of the mammalian kidney are convo- 

 luted, giving a granular appearance to the texture; while in 

 the inner part of their course they are straight, and give to 

 the texture a striated appearance. The granular outer part 

 is called the cortical portion of the kidney, and the striated 

 inner part is called the medullary portion. 



128. If a sheep's or a rabbit's kidney be examined, the cor- 

 tical substance will be seen to form a uniform layer, while the 

 straight tubules of the medullary part are gathered together 

 in one group, having the form of a ridge in the sheep, and 

 of a cone in the rabbit and the kangaroo, projecting into the 

 dilatation from which the ureter springs. 



In the porpoise each kidney consists of a large number of 



