332 THE GENITOURINARY ORGANS. 



The blood-vessels of the kidney have a characteristic distribu- 

 tion, and are in the closest relationship to the uriniferous tubules. 



The renal artery, as has been shown by Brodel, divides at the 

 hilum on an average into four or five branches, about three-fourths 

 of the blood-supply passing in front of the pelvis, while one-fourth 

 runs posteriorly. The portion of the kidney supplied by the anterior 

 branches is in its blood-supply quite distinct from that supplied by the 

 posterior branches ; the one set of branches do not cross over to the 

 other. The two ends of the kidney are supplied by an anterior 

 and a posterior branch, each of which generally divides into three 

 branches, which pass respectively, one anteriorly, one posteriorly, 

 and one around the end of the uppermost and the lowest calyx. 



The main branches of the renal artery give off lateral branches 

 to the renal pelvis, supplying its mucous membrane and then 

 breaking up into capillaries which extend as far as the "area crib- 

 rosa." The venous capillaries of this region empty into veins 

 which accompany the arteries. Besides these, other arteries origi- 

 nate from the principal branches, or from their immediate offshoots, 

 and pass backward to supply the walls of the renal pelvis, the 

 renal capsule, and the ureter. The main trunks themselves pene- 

 trate at the hilum, and divide in the columns of Bertini to form 

 arterial arches (arteriae arciformes) which extend between the cortical 

 and medullary substances. Numerous vessels, the iiitralobular 

 arteries, originate from the arteriae arciformes and penetrate into the 

 cortical pyramids between the medullary rays. Here they give off 

 numerous twigs, each of which ends in the glomerulus of a Mal- 

 pighian corpuscle. These short lateral twigs are the vasa affcrentia. 

 Each glomerulus is formed by the breaking down of its afferent 

 vessel, which, on entering the Malpighian corpuscle, divides into a 

 number of branches, five in a glomerulus of a child three months 

 old reconstructed by W. B. Johnston, each in turn subdividing into 

 a capillary net. From each of these nets the blood passes into 

 a somewhat larger vessel constituting one of the branches of the 

 efferent vessel which carries the blood away from the glomerulus. 

 Since the afferent and efferent vessels lie in close proximity, the 

 capillary nets connecting them are necessarily bent in the form of 

 loops. The groups of capillaries in a glomerulus are separated from 

 each other by a larger amount of connective tissue than separates 

 the capillaries themselves, so that the glomerulus may be divided 

 into lobules. In shape the glomerulus is spheric, and is covered 

 by a thin layer of connective tissue over which lies the inner mem- 

 brane of the capsule, the glomerular epithelium. On its exit from 

 the glomerulus the vas efferens separates into a new system of 

 capillaries, which gradually becomes venous in character. Thus, the 

 capillaries which form the glomerulus, together with the vas efferens, 

 are arterial, and may be included in the category of the so-called 

 arterial retia mirabilia. Those capillaries formed by the vas efferens 

 after its exit from the Malpighian corpuscle lie both in the medullary 



