324 



THE GENITO-URINARY ORGANS. 



lary rays, or pyramids of Ferrein, toward the surface of the kidney. 

 The latter do not, however, quite reach the surface, but terminate at 

 a certain distance below it ; they are formed by collecting tubules 

 which extend beyond the medullary substance. The entire remain- 

 ing portion of the kidney is composed of cortical substance ; be- 

 tween the medullary rays it forms the cortical processes, and at the 

 periphery of the kidney, where the medullary rays are absent, the 

 cortical labyrinth. Those portions of the cortical substance sep- 

 arating the Malpighian pyramids are known as the columns of 

 Bertini, or septa renis. 



B c 



Fig. 260. Isolated uriniferous tubules : A and B, from mouse ; C, from turtle. 

 In all three figures a represents the Malpighian corpuscle ; b> the proximal convoluted 

 tubule; c, the descending limb of Henle's loop; d, Henle's loop; e, the straight col- 

 lecting tubule ; f> the arched collecting tubule. 



The various segments of the uriniferous tubule are characterized 

 by their shape and size and by their epithelial lining. 



The Malpighian corpuscle has a diameter of from 1 20 fj. to 220 //. 

 The capsule surrounding the glomerulus consists of two layers, 

 which are to be distinguished from each other when its relation to 

 the glomerulus is taken into consideration. The capsule forms a 

 double-walled membrane around the glomerulus ; a condition 

 which is easily understood by imagining an invagination of the 



