170 THE ESSENTIALS OF HISTOLOGY 



are distributed amongst the tubules of the cortex (e) ; their blood is 

 collected by veins which accompany the arteries and join the venous 

 arches between the cortex and the medulla, receiving in their course 

 certain other veins which arise by radicles which have a somewhat 

 stellate arrangement near the capsule (vena stellula, /). 



The medulla derives its blood- supply from special offsets of the 

 arterial arches, which almost immediately break up into pencils of 

 fine straight arterioles running in groups between the straight tubules 

 of the medulla. These arterioles gradually break up into a capillary 

 network with elongated meshes which pervades the medulla (fig. 206, /), 

 and which terminates in a plexus of somewhat larger venous capillaries 

 in the papillae. From these and from the other capillaries the veins 



FIG. 207. SECTION THROUGH PART OF THE DOG'S KIDNEY. 



p, papillary, and g, boundary zones of the medulla ; c, cortical layer ; h. bundles of 

 tubules in the boundary layer, separated by spaces, 6, containing bunches of 

 vessels (not here represented), and pro'onged into the cortex as the medullary 

 rays, m ; c, intervals of cortex, composed chiefly of convoluted tubules, with 

 irregular rows of glomeruli, between the medullary rays. 



collect the blood, and pass, accompanying the straight arterioles, into 

 the venous arches between the cortex and medulla. The groups of 

 small arteries and veins (vasa recta] in the part of the medulla nearest 

 the cortex alternate with groups of the uriniferous tubules, and this 

 arrangement confers a striated aspect upon this portion of the medulla 

 (boundary zone, see fig. 207). 



The efferent vessels of those glomeruli which are situated nearest 

 to the medulla may also break up into pencils of fine vessels (false 

 arteries recta] and join the capillary network of the medulla (fig. 198, d). 



Between the uriniferous tubules, and supporting the blood-vessels, 

 is a certain amount of connective tissue (fig. 205), within which are 

 cleft-like spaces from which the lymphatics of the organ originate. 



