Chap. XVII] 



URINARY SYSTEM 



329 



(1) When the arteries reach the level of the base of the pyra- 

 mid, the branches divide laterally to form more or less com- 

 plete arches between the cortex and medulla. From the arterial 

 arches, vessels pass upward through the cortex (interlobular), 

 giving off at intervals tiny arteries, each of which enters the 

 dilated commencement or capsule of a uriniferous tubule. These 

 tiny arteries, entering the capsule, are spoken of as afferent vessels. 

 They push the thin walls of the capsule before them, break up into 

 a knot of capillary vessels, called a glomer- 

 ulus, and finally issue from the capsule as 

 efferent vessels, near the point at which the 

 afferent vessel entered. These efferent ves- 

 sels are much smaller than the afferent ves- 

 sels. They do not immediately join to form 

 veins, but break up into a close meshwork 

 or plexus of capillaries around the tubules, 

 before they unite to form the larger vessels 

 and pour their contents into the veins. 

 These veins terminate in venous arches be- 

 tween the cortex and medulla. It is in this 

 way that the cortex is supplied with blood. 



(2) The pyramids also receive their 

 blood supply from the arterial arches. The 

 blood passes downward in straight vessels 

 between the uriniferous tubules, to be re- 

 turned 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. 



It is worthy of note that, unlike the lungs and the liver, the 

 kidney receives blood from just one artery, and this blood distrib- 

 uted in different sets of vessels serves the purposes of nourish- 

 ment for the kidney substance, and the purposes of excretion. It 

 is from the capillaries of the glomeruli and the plexus of capillaries 

 around the convoluted portion of the tubules, that the passage of 

 waste material from the blood into the tubule takes place. Other 

 capillaries serve to hold the blood that is used for nourishment. 



Nerves and lymphatics. — The kidneys are well supplied with 

 nerves derived from both the sympathetic and central nervous 



Fig. 168. — Plan of 

 THE Blood-vessels con- 

 nected WITH THE Tu- 

 bules. (Note that in the 

 text the term "renal or 

 Malpighian corpuscles" is 

 ussd instead of the term 

 ' ' Malpighian body " which 

 is found on the illustra- 

 tion.) 



