viii THE EXCRETION OF URINE 423 



characteristic than that of the uriniferous tubules. The renal 

 artery given off from the aorta enters the kidney at the hilum. 

 It is exceptionally large in proportion to the size of the organ. 

 The renal vein, which leaves by the hilum, and opens directly into 

 the inferior vena cava, is still larger. Both artery and vein give 

 off a number of branches which penetrate into the substance of 

 the organ between the papillae (arteriae and venae interlobulares), 

 and form arches at the junction of the medullary and cortical 

 substance (arterial and venous arches, the latter anastomosing 



<i "->* * <.' ' '' 



^^-- 



si? 



FIG. 114. Section through fragment of human kidney at the level of Henle's intermediate zone 

 between the cortex and medulla. (Szymonowicz.) Tc, collecting tubules of Bellini ; Hd, 

 descending limb of Henle's loops ; Ha, ascending limb of Henle's loops ; Vs, blood-vessels ; c, 

 intertubular connective tissue. 



freely among themselves). The arches give off peripheral branches 

 (arteriae and venae interlobulares) which pursue a nearly straight 

 course towards the surface of the organ, and give off short and 

 usually curved branches at intervals (Fig. 115). The venous 

 branches form a capillary network, and the arterial form the vasa 

 afferentia, which penetrate into the capsule or dilated extremity 

 of the uriniferous tubules. Within the capsule the afferent vessel 

 breaks up into a much convoluted capillary mass, the vascular tuft 

 or glomerulus, which is usually divided into lobules anastomosing 

 among themselves. The glornerular capillaries unite into a single 

 efferent vessel which is always smaller than the afferent, and 

 which leaves the glomerulus close to the point at which the artery 

 enters (Fig. 116). This efferent vessel breaks up after the manner 



