URIXARY SYSTEM OF MAMMALS. 



G05 



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

 tractino; continuation to form the duct is the 



. . . 480 



' infimdibulum ;' 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.' The renal arterv, derived di- 

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

 into two or thres branches on entering the 



o 



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, , to the cortical sub- 

 stance. Here the terminal twi^s, ib. /'. enter 



O * ' 



the malpighian body, ?;/, 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 lobulated 



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, Hi/cena] or form a network 



(/%oca)upon the surface of the kidney; in all, the venous trunk, 



fig. 418, k, terminates in the postcaval, ib. A". 



The uriniferous tubule commences in Mam- 



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



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



481, in t 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 



f 



Mammalia are seen in the shape or absence of 

 the mammilla, and in their composition by a 

 seeming multiplication of simple kidneys,either 

 with or without a common cortical envelope, 



m, n p ,1 i i ,i /\ 



Hie nrst 01 these is presented by the Orni- 



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



Ttihuli urinifcri of cortical 

 and medullary part* of kid- 

 nfy. CCLXXXVl. 



181 



of m 



in Mammnlia. cxxxvn. 



