URINARY SYSTEM OF MAMMALS. 



G05 



480 



apex of the cone (where this projects), is called i calyx;' its con- 

 tracting continuation to form the duct is the 

 i infundibuluin ;' the cavity of the gland which 

 it lines, as at p, fig. 479, is the ' pelvis ' of the 

 kidney ; the fissure from which it emerges is 

 the ' hilum.V The renal artery, derived di- 

 rectly from the aorta, fig. 422, d, d, divides 

 into two or three branches on entering the 

 hilum, and, of the subdivisions of these in the 

 medullary substance, the two principal, in 

 the Kangaroo, anastomose to form an arch 

 over the base of the cone, whence proceed 

 the arterioles, fig. 481, a, to the cortical sub- 

 stance. Here the terminal twigs, ib. f, enter 

 the malpighian body, m, to form the vascular 

 brush or tuft ; the returning vessel, d, com- 

 bines, with those from other tufts, e, e, to 

 form the capillary plexus, p, which surrounds 

 the uriniferous tube, t. The capillaries unite 

 to form venules, which on the surface of the 

 human kidney have a stelliform disposition, 

 and when congested give it a finely tabulated 

 appearance. The veins from the centre of 

 each ( star ' dip into the renal substance, 

 unite, and ultimately emerge at the ' hilus ' 

 anterior to or ventrad of the artery ; but, in a 

 few Mammals, they unite in an arborescent 

 disposition (Felis, Hycena) or form a network 

 (Phoca)\x\)Q\\ the surface of the kidney; in all, the venous trunk, 

 fig. 418, k, terminates in the postcaval, ib. v. 

 The uriniferous tubule commences in Mam- 

 mals, as in lower Vertebrates (vol. ii. p. 538, 

 fig. 356), from the malpighian corpuscle, fig. 

 481, m, c, and passes toward the surface of 

 the kidney, before being reflected and convo- 

 luted in the cortical substance. 



The chief modifications of the kidneys in 

 Mammalia are seen in the shape or absence of 

 the mammilla, and in their composition by a 

 seeming multiplication of simple kidney s,either 

 with or without a common cortical envelope. 

 The first of these is presented by the Orni- 

 thorhynchus, fig. 502, a, in which the tubuli uriniferi terminate 



Tubuli uriniferi of cortical 

 and medullary parts of kid- 

 ney. CCLXXXVI. 



481 



Plan of the renal circulation 

 in Mammalia, cxxxvn. 



