198 



THE EXCRETORY SYSTEM 



between the kidney and its fascia. The kirhiey of the cat is about 

 3 cm. long by 2.5 cm. wide and 2 cm. thick; the human kidney is 

 about 11 cm. long, 6 cm. wide, and 2.5 cm. thick, with the long 

 axis parallel to the backbone. The outer margin of each kidney is 

 convex, but the mesial border presents an indentation, called the 

 hilus or hilum. Here the renal artery, renal vein, and ureter con- 

 nect with the kidney. The entire kidney is covered with a loose 

 capsule of connective tissue which is similar to the peritoneum in 

 composition. There is little connective tissue within the substance 

 of the kidneys, although the capillaries are accompanied by a rich 

 reticular network. 



Fig. 124. — Photograph of a longitudinal section of a rat's kidney, showing a 

 single papilla extending into the calyx. The darker striated region surrounding the 

 papilla (medulla) is the cortex. The adrenal is shown closely attached to the kidney 

 on the left. 



If the entire kidney is divided lengthwise into two hahes by a 

 plane parallel with the adjacent body wall, additional features can 

 be seen macroscopically. i^t the hilus can be seen the expanded 

 funnel-like continuation of the ureter, called the pehis, the internal 

 end of which is further subdivided into small funnel-like divisions, 

 called the major calyces, each of which divides into minor calyces. 

 The main collecting tubules open into the minor calyces. (Fig. 125.) 



The body of the gland is divided into two zones, an external zone 

 just within the cai)sule, called the cortex, and an inner zone, the 

 medulla, toward the pelvis. Toward the hilus of the human kidney 

 the medulla is divided into a number of triangular masses, with the 

 base of each directed toward the cortex and the apex of each fitting 

 into a minor calyx of the pelvis. These triangular appearing masses 

 are known as renal pyramids and are in reality conical masses of 



