PHYSIOLOGICAL ANATOMY OF THE KIDNEYS 329 



their course, becoming reduced in number until they open at the apices 

 of the pyramids into the infundibula and the pelvis of the kidney. 



Distribution of Bloodvessels in the Kidney. The renal artery, which 

 is quite voluminous in proportion to the size of the kidney, enters at 

 the hilum and divides into four branches. A number of smaller 

 branches penetrate between the pyramids and ramify in the columns 

 of cortical substance that occupy the spaces between the pyramids 

 (columns of Bertin). The main vessels, which usually are two in num- 

 ber, occupy the centre of the columns of Bertin, sending off in their 

 course at short intervals regular branches on either side toward the 

 pyramids. When these branches reach the boundary of the cortical 

 substance they turn upward and follow the periphery of the pyramid 

 to its base. Here the vessels form an arched anastomosing plexus, the 

 arterial arcade, situated between the rounded base of the pyramid and 

 the cortical substance. This plexus presents a convexity looking toward 

 the cortical substance, and a concavity, toward the pyramid. It is so 

 arranged that the interstices are just large enough to admit the collec- 

 tions of tubes that form the pyramids of Ferrein. 



From the arterial arcade, branches are given off in two opposite 

 directions. From its concavity, small branches, measuring at first 

 T^Vo to yi"o f an mc ^ ( 2I to 34- /*) m diameter, pass downward 

 toward the papillae, giving off small ramifications at very acute angles 

 and becoming reduced in size to about -^Vo of an inch (lo/x). These 

 vessels, called the arteriolae rectae, surround the straight tubes and pass 

 into capillaries in the substance of the pyramids and at their apices. 



From the convex surface of the arterial arcade, branches are given 

 off at nearly right angles. These pass into the cortical substance, 

 breaking up into a number of little arterial twigs, yg 1 ^ to $%-$ of an 

 inch (17 to 40 ft) in diameter, each one of which penetrates a Mal- 

 pighian body at a point opposite the neck of the capsule. Once within 

 the capsule, the arteriole breaks up into five to eight branches, which 

 then divide dichotomously into vessels measuring 3^^ to YsVo" f an 

 inch (8 to 17 p) in diameter, arranged in the form of coils and loops, 

 constituting a dense rounded mass (the Malpighian coil, or glomerulus), 

 filling the capsule. These vessels break up into capillaries without 

 anastomoses (see Plate VII, Fig. 4). 



The blood is collected from the vessels of the Malpighian bodies by 

 a vein, which passes out of the capsule by the side of the arteriole and, 

 with veins from other glomeruli, forms a plexus closely surrounding the 

 convoluted tubes. This is a true plexus, the branches anastomosing 

 freely in every direction ; and the distribution of vessels in this part 

 resembles essentially the vascular arrangement in most of the glands. 



