184 ANATOMY FOR NUESES. [CHAP. XVI. 



sels. These efferent vessels do not immediately join to form 

 veins, but break up into a close meshwork of capillaries around 

 the tubules, before they unite to form the larger vessels and 

 pour their contents into the veins forming the venous arches, 

 between the cortex and medulla. In this way the cortex of 

 the kidney is supplied with blood. The medulla also receives 

 its blood-supply mainly from the arterial arches. The blood 

 passes downwards in straight vessels between the uriniferous 

 tubules, to be returned by more or less straight veins to the 

 venous arches, whence it is conveyed by large branches into 

 the renal vein, which leaves the kidney at the hilus and pours 

 its contents into the inferior vena cava. 



The renal artery in passing into the kidney is accompanied 

 by a network of nerves, called the renal 

 plexus. They are chiefly vaso-motor nerves, 

 and regulate the contraction and relaxation 

 of the renal blood-vessels. 



Secretion of urine. Urine is secreted 

 from the blood in two ways. It is partly 

 removed by a process of transudation or fil- 

 tration, and partly by the secretory action 

 of the cells lining the uriniferous tubules. 



(1) Into the dilated extremity or capsule 

 of each tubule a small artery enters and, 



pushing the wall of the capsule before 

 FIG. 108. PLAN OF THE . i ? . . i i i j -i 



BLOOD VESSELS CONNECT- lt Drea ks up into a bunch of looped capll- 



ED WITH THE TUBULES. lanes. The blood in the loop of capillaries 

 or glomerulus is only separated from the 



interior of the tubule by the thin walls of the capillaries and 

 the inverted wall of the capsule, which closely covers the 

 glomerulus. The artery entering the capsule is larger than 

 the issuing vein, and, during its passage through the glom- 

 erulus, the blood is subjected to considerable pressure. As a 

 result of this, a transudation of the watery constituents of the 

 blood, with some dissolved salts, takes place through the walls of 

 the blood-vessels and of the capsule into the tubule. 



(2) After leaving the capsule, the efferent vein breaks up 

 into a meshwork of capillaries, which closely surrounds the 

 tubules, so that the blood is again brought into close communi- 

 cation with the interior of the tubules. The tubules are lined 



