KIDNEY. 



[ 447 ] 



KIDNEY. 



masses or pyramids, converging towards the 

 hilum, and their apices forming the papillae ; 

 whilst the cortical substance constitutes the 

 outer part of the organ, and fills up the in- 

 terstices between the pyramids. Micro- 

 scopically examined, the cortical part also 

 becomes resolved into as many segments as 

 there are pyramids ; hence the kidneys may 

 be regarded 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 on the surface of 

 the papilla?, and pass through the pyramids, 



Fig. 382. 



finally becoming again tortuous and enlarged 

 before terminating in the Malpighian cap- 

 sules. 



Fig. 383. 



Papilla of the kidney of a pig with the tubules in- 

 ected, showing their origins upon the surface. 

 Magnified 10 diameters. 



running straight and nearly parallel with 

 each other (fig. 383 k). During this course 

 they undergo repeated dichotomous subdi- 

 vision (fig. 383 /), the branches being given 

 off at a very acute angle, and at first with 

 considerable diminution in size ; and some- 

 times they divide into threeorfourbrancb.es, 

 so that ultimately a larger bundle of tubes 

 proceeds from them, producing the increased 

 breadth of the pyramids towards the exte- 

 rior. Towards the base of the pyramids, 

 the parallel tubules become more loosely 

 connected by the interposition of bundles 

 of arteries and veins (which run straight), 

 and they diverge in all directions, pursuing 

 an undulating course. 



On reaching the cortex, the tubules 

 branch off and increase in diameter, becom- 

 ing also very tortuous ; then they turn back, 

 diminishing in breadth, and run parallel 

 with their first course, but in the opposite 

 direction. They then form a curve, the 

 loop of Henle, and run upwards again, 



Perpendicular section of the injected kidney of a rab- 

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

 of the vessels, on the right that of the tubules is shown. 

 a, interlobular arteries, with their Malpighian tufts b, 

 and vasa efferentia c ; d, capillaries of the cortical por- 

 tion ; e, vasa efferentia of the outermost tufts, passing to 

 the surface of the kidney ; f, vasa efferentia of the in- 

 nermost tufts, running into the straight arteries, a, g, g ; 

 h, capillaries of the pyramids, arising from the latter ; 

 i, a straight vein commencing at the papilla ; k, 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 Mal- 

 pighian capsules. 



Magnified 30 diameters. 



The urinary tubules are cylindrical, and 

 usually consist of a basement membrane 



