334 THE ORGANS 



After leaving the glomerulus, the efferent vessel breaks up into a 

 second system of capillaries, which form a dense network among the 

 tubules of the cortical pyramids and of the medullary rays. The 

 mesh corresponds to the shape of the tubules, being irregular in the 

 pyramids, long and narrow in the rays. In these capillaries the blood 

 gradually becomes venous and passes into the interlohular veins (Fig. 

 230, c). These accompany the interlobular arteries to the boundary 

 between cortex and medulla, where they enter the arcuate veins, which 

 accompany the arcuate arteries (Fig. 230, d). 



The main arteries to the medulla arise from the inner concave sides 

 of the arterial arches. They pass straight down among the tubules 

 of the medulla and are known as arterice rectce. Branching, they give 

 rise to a long-meshed capillary network which surrounds the tubules. 

 This capillary network is also supplied by (i) efferent vessels from 

 the more deeply situated glomeruli (false arteri^ rectae) and (2) by 

 medullary branches from the interlobular arteries. The veins of the 

 medulla arise from the capillary network and follow the arteries 

 back to the junction of medulla and cortex, where they empty into 

 the arcuate veins (Fig. 230, d). 



In addition to the distribution just described, some of the inter- 

 lobular arteries extend to the surface of the kidnev, where thev enter 

 the capsule and form a network of capillaries which anastomose with 

 capillaries of the suprarenal, recurrent, and phrenic arteries. A 

 further collateral circulation is estabhshed bv branches of the above- 

 named arteries penetrating the kidney and forming capillary networks 

 within the cortex, even supplying some of the more superficial 

 glomeruli. The most superficial of the small veins which enter the 

 interlobular are arranged in radial groups, having the interlobular 

 veins as their centres. These lie just beneath the capsule, and are 

 known as the stellate veins oj Verheyn. In addition to capillary 

 anastomoses, direct communication between arteries and veins of 

 both cortex and medulla, by means of trunks of considerable size, 

 has been described. 



The lymph vessels of the kidney are arranged in two systems, a 

 superficial system which ramifies in the capsule, and a deep system 

 which accompanies the arteries to the parenchyma of the organ. 

 Little is known of the relation of the lymphatics to the kidney tubules. 



Nerves. — These are derived from both cerebro- spinal and sym- 

 pathetic S3'stems. The medullated fibres appear to pass mainly to 

 the walls of the blood-vessels which supply the kidney capsule. 



