BLOOD VESSELS OF THE KIDNEY. 257 



around the vessels, in the papillae, and about the renal corpuscles than 

 elsewhere. The normal amount should be carefully studied since an 

 increase in this "interstitial tissue" is indicative of disease. 



Lobes and lobules. In embryonic life the kidney is divided into lobes, 

 bounded by the renal columns and indicated by grooves upon the outer 

 surface (Fig. 290). The grooves become obliterated during the first year. 

 (In the ox similar grooves are permanent; in most mammals they never 

 exist, as the kidney has but one lobe, papilla and pyramid.) The lobules 

 or structural units of the kidney are the areas centering around each ra- 

 diate division of the cortex, by which they are drained. They are not 

 bounded by connective tissue septa. 



Blood vessels. The kidney has a capillary circulation. The renal 

 artery, from the aorta, passes to the hi! us or notch on the medial 

 border of the kidney. It divides into several branches 

 most of which pass over the ventral surface of the 

 pelvis into the fat around the calyces (Fig. 281). As 

 intcrlobar arteries they pass to the boundary layer be- 

 tween the cortex and medulla where they are designated 

 arciform arteries (Fig. 291). These send interlobular 

 arteries through the convolute part of the cortex and 

 their terminal branches enter the fibrous capsule. It 

 will be noted that the kidney is exceptional in having 



' FIG. 290. -KIDNEY OF 



its arteries at the periphery of its lobules. From the A CHILD AT BIRTH. 



* (After Hertwig.) 



interlobular arteries small stems pass to the glomcr- 

 uli, each of which receives a single twig (Fig. 292). This is resolved 

 into a knot of capillary loops, the endothelium of which seems to blend 

 with the surrounding syncytium and possibly with the inner layer of the 

 capsule. The glomerulus often appears lobed, due to the arrangement 

 of its vascular loops. The capillaries unite to form a single efferent vessel 

 which divides into small branches on leaving the capsule. These spread 

 among the convoluted and straight tubules of the cortex and some continue 

 into the medulla. The latter is supplied by other straight branches 

 (arteriolae rectae) from the interlobular, efferent and arciform arteries as 

 shown in Fig. 291. The veins of the medulla begin around the papillae 

 and as vcnulac rectae empty into the arciform veins. The cortical veins are 

 the interlobular vessels which are beside the corresponding arteries. They 

 arise from converging veins in the renal capsule which on surface view 

 form a stellate figure (venae stellatae). The interlobular veins drain the 

 capillaries of the cortex, but have no direct relation with the glomcruli. 

 Intcrlobar veins follow the arteries, passing out from the hilus of the 

 kidney over the ventral surface of the renal pelvis. 

 17 



