THE URINARY TRACT. 



735 



The afferent vessel is either a terminal branch of the renal 

 artery or a lateral offshoot of snch a branch, which is given off 

 without any regularity. Not infrequently the afferent vessel 

 assumes a backward course, 

 especially near the region 

 lying between cortex and 

 pyramid, in human as well 

 as in dogs' kidneys. The 

 ultimate terminations of 

 the arteries and their tufts 

 never reach the outermost 

 portion of the cortical sub- 

 stance, which is supplied 

 with capillaries only. 



The afferent artery in- 

 variably exhibits a distinct 

 middle or muscle coat, and 

 splits abruptly into a num- 

 ber of capillaries, which 

 contain arterial blood, and, 

 by being convoluted and 

 turned upon themselves, 

 produce the tuft. According 

 to C. Ludwig the formation 

 of the tuft is easily under- 

 stood by assuming that the 

 arterial bed of the afferent 

 vessel is abruptly widened 

 and at the same time split 

 into a number of very 

 narrow (capillary) canals, 

 which again unite into the 

 efferent vessel : bring the 

 surface of the opposite FIG. 329. CORTICAL SUBSTANCE OF THE 



KIDNEY OF A DOG. BLOOD-VESSELS 

 INJECTED. 



S 



Ca, capsule ; O, outer zone, devoid of tufts ; T r 



parts together, so that the 

 afferent and efferent ves- 

 sels are in proximity, and 



. 1 _., tuft; A, afferent vessel; E, efferent vessel; _R 



the tutt IS Complete. Ihe branch of renal artery; Co, zone of convoluted 

 prkT'ma+irk-n nan Vn Taar1ilTr tubules; 8, zone of straight tubules (medullary 



loi ma iion can oe reaciiiy . ' . , inn ,. 



* ray). Magnified 100 diameters. 



demonstrated with a hand- 

 kerchief, the two compressed ends of which are held in the two 

 hands, one representing the afferent, the other the efferent vessel y 



