KIDNEY. 



[ 373 ] 



KIDNEY. 



ing n fat ; and a tunica propria, or albu- 

 ginea, which forms a whitish, thin, but firm 

 membrane, closely surrounding the kidney, 

 becoming connected with the pelvis and 

 vessels at the hilus, without being prolonged 

 into the interior of the organ, and consisting 

 of ordinary areolar tissue with numerous 

 fine networks of elastic tissue. 



The parenchyma, in a transverse section, 

 appears to the naked eye to consist of two 

 parts, the inner or tubular substance, and 

 the outer or cortical. The tubular substance 

 is composed of 8-15 isolated conical masses 

 or pyramids, converging towards the hilus, 

 and then* apices forming the papilla ; whilst 

 the corticp.1 substance constitutes the outer 

 part of the organ, and fills up the interstices 

 between the pyramids. When microscopic- 

 ally examined, the cortical part also becomes 

 resolved into as many segments as there are 

 pyramids; hence the kidneys may be re- 

 garded as composed of a certain number of 

 intimately connected lobules. 



Both the cortical and the tubular substance 

 consist principally of the urinary tubules. 

 These commence in each segment or lobule 

 by very numerous orifices in the surface of 



Fig. 386. 



Papilla of the kidney of a pig with the tubules injected, 

 showing their origins upon the surface. 

 Magnified 10 diameters. 



the papillae, and pass through the pyramids, 

 running straight and nearly parallel with 

 each other (fig. 387 &) During this course 

 they undergo repeated dichotomous subdi- 

 vision (fig. 387 I), the branches being given 

 off at a very acute angle, and at first with 

 considerable diminution in size ; and some- 

 times they divide into three or four branches, 

 so that ultimately a larger bundle of tubes 

 proceeds from them, producing the increased 

 breadth of the pyramids towards the exterior. 



Towards thebase of the pyramids, theparallel 

 tubules become more loosely connected by 



Fig. 387. 



Perpendicular section of the injected kidney of a rabbit 

 through part of a pyramid. On the left the course of the 

 vessels, on the right that of the tubules is shown, a, in- 

 terlobular arteries, with their Malpighian tufts b, and 

 vasa efferentia c ; d, capillaries of the cortical portion ; 

 e, vasa efferentia of the outermost tufts passing to the 

 surface of the kidney ; /, vasa efferentia of the innermost 

 tufts running into the straight arteries, g,g,g; h, capil- 

 laries of the pyramids arising from the latter ; i, a straight 

 vein commencing at the papilla; A, origin of a urinary 

 tubule at a papilla ; I, o, branches of the same ; m, coiled 

 portion in the cortex ; n, the same at the surface of the 

 kidney; p, connexion with the Malpighian capsules. 



Magnified 30 diameters. 



the interposition of bundles of arteries and 

 veins, which run straight, and they diverge 



