KIDNEY. 



[ 374 ] 



KIDNEY. 



in all directions, pursuing an undulating 

 course. On reaching the cortical substance, 

 this is still more the case, and the tubules 

 become inextricably interwoven, each finally 

 terminating in a Malpighian body. Those 

 which have not terminated in a Malpighian 

 body before reaching the surface of the kid- 

 ney, are reflected inwards until they do so ; 

 hence on viewing the outer surface of an 

 injected kidney, the loops of these tubules 

 are seen. 



The urinary tubules are cylindrical, and 

 consist of a basement membrane (fig. 388 b) 

 lined with pavement epithelium, c?. The base- 

 ment membrane is very transparent, but firm 

 and elastic. Within it is a single layer of 

 nucleated polygonal epithelial cells (fig. 388 

 d, e). These, when immersed in water, lose 

 their polygonal form, become rounded, and 

 appear to fill up the tubules entirely ; they 

 often also burst, and then the tubules appear 

 to contain nothing more than a finely gra- 

 nular mass with nuclei. These changes are 

 found to have taken place spontaneously, if 

 the kidney be not fresh. The epithelial cells 

 are larger in the convoluted than in the 

 straight tubules (fig. 388, 2). 



1 . A Malpighian body, A, with the urinary tubule B, C; 

 human, a, Capsule of the Malpighian body, continuous 

 with b, the basement-membrane of the tubule ; c, epi- 

 thelium of the Malpighian body ; d, that of the tubule ; 

 e, detached epithelial cells ; /, afferent vessel ; g, efferent 

 vessel; //, Malpighian tuft. 2. Three epithelial cells 

 from coiled tubules, one of them containing globules of 

 fat. 



Magnified 300 diameters. 



The Malpighian bodies may be regarded 

 as terminal dilatations of the tubules, each 

 containing a round plexus of vessels, the 

 Malpighian tuft. 



The basement membrane surrounding the 

 tuft (fig. 388 a) is somewhat thicker than 

 elsewhere, and the epithelium lining it is 

 continued over the free surface of the tuft. 

 The Malpighian tufts consist of close convo- 

 lutions of fine vessels derived from branches 

 of the renal artery. The latter enter the 

 kidney between the pyramids, and continue 

 to divide until arriving at the cortical sub- 

 stance, where they give ofi' a number of long 

 branches, mostly running towards the con- 

 vex surface of the kidney, between the lo- 

 bules, hence called interlobular arteries. 

 From these short, mostly lateral branches 

 are given off, each of which terminates in a 

 Malpighian tuft, forming its afiferent vessel. 

 Each afi^erent vessel, on entering the Mal- 

 pighian body, divides into 5-8 branches, each 

 of which becomes subdivided into a tuft of 

 capillaries; these are variously convoluted 

 and interwoven, ultimately uniting to a sin- 

 gle vessel, the efferent vessel. The afferent 



Fig. 389. 



From a human kidney, a, end of an interlobular ar- 

 tery ; b, afferent vessels ; c, naked Malpighian tuft ; 

 d, efferent vessels ; e, tufts enclosed in their capsules ; 

 /, urinary tubules arising from them. 



Magnified 45 diameters. 



