G04 



ANATOMY OF VERTEBKATES. 



CHAPTER XXX1Y. 



URINARY SYSTEM OF MAMMALS. 



356. Kidneys of Mammals.- -These glands (fig. 422, o, o, and 

 vol. ii. fig. 139, k) are characterised, in the present class, by 

 being composed of two kinds of substance differing in colour ; one 

 ' cortical,' highly vascular, with tortuous secerning tubes, fig. 479, 

 c ; the other ( medullary,' less vascular, with straight secerning 

 tubes, ib. m. They are preceded, in the development of Mam- 

 mals, as of Birds, by the temporary embryonal bodies, noticed and 

 figured in vol. ii. p. 226, fig. 103 : but the persistent kidneys 

 reach a higher grade of structure, differentiated as above. They 

 have a more compact and definite form than in birds, and their 

 vascular supply is more exclusively their own ; the uriniferous 

 tubules converge toward the interior, and do not spread to the 

 exterior, of the gland ; the ureter, moreover, is not directly con- 

 tinued from them, but receives, by a dilated beginning or pelvis, 

 7?, their terminations usually crowded upon a prominence called 

 6 mammilla.' All mammals have the urinary bladder. 



In Lyencepliala, lAssencepliala, and most of the smaller species 

 of Gyrencephala, the kidney offers its most simple mammalian con- 

 dition, as exemplified in fig. 479. The 

 cortical substance, of softer texture, 

 and usually of a dull light-red colour, 

 contains the malpighian bodies, fig. 

 481, m, c (vol. i. p. 538), and the re- 

 flected tortuous beginnings of the uri- 

 niferous tubes, ib. t : the medullary 

 substance is firmer, of less uniform 

 colour, conical in form, dark red at the 

 base, lighter-coloured toward the apex 

 in many Mammals ; it is devoid of mal- 

 pighian bodies, and is composed chiefly 

 of the urimferous tubes continued from the cortical part in a 

 straighter course, uniting as at y, s, , fig. 480, on the dichoto- 

 mous plan, and converging to open upon the apex of the medul- 

 lary cone. 



The membranous beginning of the ureter, reflected upon the 



479 



Type of Mammalian kidney. 



