THE KIDNEY. 185 



the cortex and medulla. From the convex side of 

 the arterial trunks spring numerous small branches, 

 each of which enters at once the apex of a cortical 

 pyramid, and proceeds directly toward the surface 

 of the organ ; these arteries are called interlobular 

 arteries* From these interlobular arteries lateral 

 twigs are given off at frequent intervals, which, after 

 passing a short distance, enter the glomeruli, as the 

 arteriae afferentes. On leaving the glomerulus, the 

 efferent vein which still carries arterial blood 

 breaks up into a capillary net-work, which lies 

 among the adjacent convoluted tubules and in the 

 neighboring medullary rays, the meshes in the for- 

 mer region being rounded, in the latter, elongated, 

 corresponding to the character of the tubules among 

 which they lie. From these the blood is collected 

 into small veins, which in turn pour it into interlob- 

 ular veins, and these, following the course of the 

 interlobular arteries, finally pour it into the large 

 arched trunks. between the cortex and medulla. In 

 the superficial portions of the cortex there are no 



* If we consider a circumscribed portion of the cortex of the kid- 

 ney, having for its centre a medullary ray, and extending on every 

 side as far as to the nearest interlobular vessels, we see that in this 

 limited area we have all of the essential structural elements of the 

 cortex a medullary ray surrounded by convoluted tubules and glomer- 

 uli. Such groups of elements, although they have by no means a 

 separate existence, and can be but indefinitely bounded, have been 

 called lobuli ; and, hence, the vessels passing between them are 

 termed interlobular vessels. 



