738 



THE UEINAEY TRACT. 



The ascending branches of the arterial arches which give rise 

 to the afferent vessels are, by most authors, termed inter-lobular 

 arteries. This, name should be abandoned, for the reason that 

 they occupy the center of a cortical lobule (Lud wig's labyrinth). 

 The capillaries of the cortical substance are usually considered 

 to be of two kinds those rising directly from the efferent ves- 

 sels, for the supply of the 

 medullary rays, and those of 

 the labyrinth, which are pro- 

 longations of the former. 

 This conception is, however, 

 misleading, inasmuch as the 

 efferent vessels produce the 

 capillaries of the labyrinth 

 and the medullary rays, both 

 directly and indirectly, and 

 there is no necessity for 

 speaking of arterial and 

 venous capillaries. Fig. 329 

 shows the distribution of 

 the capillaries from the ef- 

 ferent vessels, some running 

 first to the labyrinth, others 

 first to the medullary rays. 



The veins arise from the 

 capillaries of the cortical 

 substance, especially those 

 of the labyrinth, and their 

 confluence is often marked 

 on the surface of the kid- 

 ney in the form of stars 

 (stellulae Verheyenii). As 

 the medullary rays are lost 

 near the surface of the kid- 

 ney, and the outermost por- 



tion of the COrteX has nO 



tufts, obviously the veins 



the capillaries of the cortical substance ; , bun- arise from the CapillarV SVS- 

 dle of vasa recta. Magnified 100 diameters. 



tern surrounding the con- 

 voluted tubules. The veins accompany the arteries, and empty 

 into the venous plexus at the boundary zone between the cortex 

 and the pyramis. The latter furnishes veins derived both from 



FIG. 332. BOUNDARY ZONE BETWEEN 

 THE CORTICAL AND PYRAMIDAL SUB- 

 STANCE OF THE KIDNEY OF A DOG. 

 BLOOD-VESSELS INJECTED. 



A, branch of renal artery; Co, prolongation of 



