REN. 



237 



presenting an irregular granular surface. In 

 an injected specimen there may be seen scat- 

 tered through the cortical substance, in every 

 part, except near the surface of the organ, 

 numerous minute red granules; these bodies 

 have been named after the distinguished ana- 

 tomist who discovered them, the Malpighian 

 bodies of the kidney. The great mass of the 

 cortical substance is made up of secreting 

 tubules, the existence of which was first 

 clearly demonstrated by Ferrein; hence they 

 have been named the tubes of Ferrein. The 

 course of these tubes is, for the most part, 

 very tortuous; but near the basis of what will 

 presently be described as the pyramids of 

 Malpighi there is an appearance, visible even 

 to the naked eye, of straight lines radiating 

 towards the surface of the kidney ; these lines 

 result from bundles of tubes passing upwards 

 from the pyramids of Malpighi and retaining 

 their straight course until they reach the sur- 

 face, where they become tortuous, and pass 

 backwards deeply into the cortical substance 

 (fig. 143). 



The surface of the cortical portion fre- 

 quently presents an appearance of lobules, some- 

 what similar to those of the liver. The form 

 of these lobules varies considerably ; in some 

 instances they are circular, but very com- 

 monly they have a pentagonal or hexagonal 

 outline ; they are usually about \ of an inch in 

 diameter (fig. 144). 



Fig. 144. 



Portion of the surface of the kidney, showing the 

 lobulated appearance which results from congestion 

 of the venous radicles. Natural size ; from a speci- 

 men prepared by Mr. Bowman. 



This lobulated appearance of the surface is 

 produced by the venous radicles which are 

 dispersed at nearly equal distances throughout 

 the cortical substance, each receiving the 

 blood, as will presently be shown, from 

 the plexus surrounding the convoluted tubes. 

 These radicles unite in an irregularly arbores- 

 cent figure, anastomose, and form the several 

 branches of the renal vein. Those on the sur- 

 face have a tendency to converge towards a 

 central vessel, which then dips into the interior 

 to join the trunks of the renal vein. Thus 

 are formed the stellated vessels, which are 

 often very conspicuous in diseased specimens, 

 when there has been an impeded circulation 

 through the veins of the kidney. Between 

 the arms of these stellae the convoluted tubes 

 are visible on the surface (fig. 145). Ferrein 

 supposed each of these lobules to form the 

 base of a pyramid, the apex of the same 

 being at the extremity of a mamillary process, 

 and he believed that such an elongated pyra- 



mid might be traced continuously from one 

 part to the other, the tissues radiating from 



Fig. 145. 



Portion of the surface of the human kidney in- 

 jected by the artery, t, t, tortuous tubes as seen on 

 the surface; p, capillary plexus surrounding the 

 tubes; e, a branch of one of the stelliform veins. 

 Magnified forty-five diameters. (After Bowman.) 



a point in the mamillary process, through 

 the cortical substance, to one of the lobular 

 divisions on the surface. Mr. Bowman's 

 preparations show that " each lobule contains 

 many tortuous ducts with their capillaries, but 

 the convolutions of any one duct are not 

 confined to a single lobule." Hence it is ma- 

 nifest that there is no natural division of the 

 renal substance corresponding with the sup- 

 posed " pyramids of Ferrein," and there 

 appears no reason for retaining a name which 

 is not expressive of any fact or definite idea. 



The medullary substance or, as it is some- 

 times called, the tubular portion, is of a firmer 

 texture and darker red colour than the cortical 

 portion, and presents itself under the form of 

 cones or pyramids, (pyramids of Malpighi,) 

 the bases of which are directed towards the 

 surface of the kidney and continuous with 

 the cortical portions, while the apices, which 

 are called mamillary processes, or papillce, are 

 free and directed towards the cavity of the 

 pelvis. The number of these pyramids has 

 been variously stated by different anatomists ; 

 their number is not constant, but it is usually 

 about twelve or fifteen in each kidney. Some 

 of the pyramids are compound, being formed 

 by the union of two, which have one com- 

 mon mamillary termination. The number of 

 mamillary processes is therefore less, by 

 four or six, than that of the pyramids. The 

 cut surface of each pyramid has a striated 

 appearance, being composed of tubes which 

 subdivide and radiate in passing from the apex 

 towards the base, where they merge into the 

 cortical substance. These tubes are com- 



