ANATOMY OF THE KIDXEYS. 161 



vessels, the straight tubes of the pyramidal substance, and 

 the tubes and Malpighian bodies of the cortical substance. 



The renal artery penetrates the kidney at the hilum, 

 sends branches between the pyramids, which are distributed 

 in the form of an arched arterial plexus over the upper por- 

 tion and the bases of the pyramids, following exactly the 

 boundary between the pyramidal and the cortical substance. 

 From these vessels, branches are given off both on the con- 

 vexity and the concavity of the arches. JSTumerous small 

 branches (arteriolse rectse) pass downward along the straight 

 tubes toward the papillae, becoming capillary as they sur- 

 round the tubes. Other branches take an opposite direc- 

 tion and pass into the cortical substance, breaking up into 

 little twigs, each one of which penetrates a capsule of Muller 

 and divides in its interior into a mass of looped, convoluted 

 vessels which constitute the Malpighian coil. The blood 

 is carried away from the Malpighian bodies by one, two, or 

 three vessels, which are then immediately distributed in a 

 close plexus around the tubes of the cortical substance. 

 From this plexus, the radicles of the renal vein pass to the 

 surface of the kidney, where they present a stellate arrange- 

 ment, converging toward several large central vessels (the 

 stars of Yerheyen). These central vessels penetrate the cor- 

 tical substance and form an arched venous plexus over the 

 rounded bases of the pyramids. This plexus also receives by 

 its concave surface venous branches from the pyramidal 

 substance. The blood is then emptied into larger veins, 

 passing between the pyramids in the same sheath with the 

 arteries, to form the renal or emulgent vein. 



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