STRUCTURE OF THE KIDNEY 195 



neys and is about J inch thick. It is reddish and granular in 

 appearance. From it pass in between the Malpighian pyra- 

 mids columns known as the columns of Berlin. The cortical 

 substance contains the glomeruli and convoluted tubules to- 

 gether with blood-vessels and lymphatics supported by con- 

 nective tissues. 



The pyramidal substance, also called the medullary sub- 

 stance, consists of a number of pryamids, 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 pyramid, so that the very large 

 number entering the base is represented by only 10-25 a * ^ ne 

 apex. Thus it is that the Malpighian pyramid is divided into a 

 number of smaller pyramids. These latter are the pyramids of 

 Ferrein, and correspond in number to the number of tubes radi- 

 ating from the apex of the larger pyramid. The medullary 

 substance is marked by striae which have the direction of the 

 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 y-J-o-^ir inch in diameter. They con- 

 sist of a bunch of capillaries in the shape of a ball, the glomerulus, 

 surrounded by the extremity, or rather the beginning, of one of 

 the renal tubules. At the point where the tubule joins the Mal- 

 pighian tuft it is constricted; running then over the glomerulus 

 it reaches the afferent artery and the efferent vein on the oppo- 

 site side; when it has reached these vessels it is reflected over 

 the whole network of capillaries so that really the tuft is outside 

 the tube, but practically it is covered by a doable layer of the 

 tube wall. A space, the beginning of the tubule, is left between 

 these two layers and into it the glomerular secretion passes. The 



