326 



THE ORGANS 



medullary or Malpighian pyramid (Fig. 223). The extensions down- 

 ward of cortical substance between the Malpighian pyramids con- 

 stitute the columns of Bertini or septa renis (Fig. 222, /). Radiating 

 lines — medullary rays or pyramids of Ferrein — extend outward from 

 the base of each Malpighian j)yramid into the cortex (Fig. 222.) As 

 the rays extend outward in groups they outline pyramidal cortical 

 areas. These are known as the cortical pyramids or cortical labyrinths 

 (Fig. 223). 



The secreting portion of the kidney is composed of a large number 

 of long tortuous tubules, the uriniferous tubules. 



Each URINIFEROUS TUBULE begins in an expansion known as 

 Bowman's capsule (Figs. 223, BC, and 224, 3, 4, 5). This encloses a 



Fig. 224. — Diagrams Illustrating Successive Stages in Development of the Renal 

 Corpuscle, i and 2, Approach of blood-vessel and bhnd end of tubule; 3, invagination of 

 tubule by blood-vessels; 4 and 5, later stages, showing development of glomerulus and of 

 the two-laj'ered capsule of the renal corpuscle, the outer layer being the capsule of 

 Bowman continuous with the epithelium of the first convoluted tubule. 



tuft of blood capillaries, the glomerulus. Bowman's capsule and the 

 glomerulus together constitute the Malpighian body or renal corpuscle 

 (Fig. 225). As it leaves the Malpighian body the uriniferous tubule 

 becomes constricted to form the neck (Figs. 223, N, 224, and 225, h). 

 It next broadens out into a greatly convoluted portion, the first con- 

 voluted tubule (Fig. 223, PC, and Fig. 226). The Malpighian body, 

 the neck, and the first convoluted tubule are situated in the corti T 

 pyramid (Fig. 223). The tubule next takes a quite straight courst" 

 downward into the medulla — descending arm of Henle's loop (Fig. 223, 

 D) — turns sharply upon itself — Henle's loop (Fig. 223. L)— and passes 

 again toward the surface — ascending arm of Henle's loop (Fig. 223, 

 A) — through the medulla and medullary ray. Leaving the medullary 

 ray, it enters the same cortical pyramid from which it took origin to 

 become the second convoluted tubule (Fig. 223, DC). This tubule is in 



