STRUCTURE OF THE KIDNEY 195 



The cortical substance constitutes the outer layer of the 

 kidneys and is about % inch thick. It is reddish and granu- 

 lar in appearance. From it pass in between the Malpighian 

 pyramids columns known as the columns of Bertin. The 

 cortical substance contains the glomeruli and convoluted tu- 

 bules together with blood-vessels and lymphatics supported 

 by connective tissues. 



The pyramidal substance, also called the medullary sub- 

 stance, consists of a number of pyramids, about 12-15, whose 

 bases look outward and rest on the cortical substance and 

 whose apices look inward and are received into the calyces. 

 These are called the pyramids of Malpighi. They contain 

 uriniferous tubules, vessels, etc., supported by connective 

 tissue. It will be seen that these tubes converge and join 

 each other in passing from the base to the apex of the pyra- 

 mid, so that the very large number entering the base is rep- 

 resented by only 10-25 at the apex. Thus it is that the Mal- 

 pighian pyramid is divided into a number of smaller pyra- 

 mids. These latter are the pyramids of Ferrein, and cor- 

 respond in number to the number of tubes radiating from 

 the apex of the larger pyramid. The medullary substance is 

 marked by striae which have the direction of tubules and 

 which are caused by them. Its consistence is firmer and its 

 color is darker than that of the cortical substance. 



Malpighian Bodies. These are scattered throughout the 

 cortical substance, and are M.oo-^50 inch in diameter. They 

 consist of a bunch of capillaries in the shape of a ball, the 

 glomerulus, surrounded by the extremity, or rather the be- 

 ginning, of one of the renal tubules. At the point where the 

 tubule joins the Malpighian tuft it is constricted; running 

 then over the glomerulus it reaches the afferent artery and 

 the efferent vein on the opposite side ; when it has reached 

 these vessels it is reflected over the whole network of capil- 

 laries so that really the tuft is outside the tube, but practic- 

 ally it is covered by a double layer of the tube wall. A space, 

 the beginning of the tubule, is left between these two layers 



