THE URINARY ORGANS. 323 



V. THE GENITO-URINARY ORGANS. 

 A. THE URINARY ORGANS. 



J. THE KIDNEY. 



THE kidney is a branched tubular lobular gland, which in man 

 consists of from ten to fifteen nearly equal divisions of pyramidal 

 shape known as the renal lobes. The apex of each pyramid (the 

 Malpighian pyramid) projects into the pelvis of the kidney. The 

 kidney is surrounded 

 by a thin but firm cap- 

 sule consisting of fib- 

 rous connective tissue a --T^P^t^S^P^IlByi^lP^ Artery< 

 containing a few elas- 

 tic fibers and, in its Vein. _. 

 deeper portion, a thin 

 layer of nonstriated 



muscle-cells Fig * 2 59- Kidney of new-born infant, showing a 



'* . distinct separation into reniculi ; natural size. At a is 



The secreting por- seen the consolidation of two adjacent reniculi. 



tion is composed of a 



large number of tubules twisted and bent in a definite and typical 

 manner, the uriniferous tubules. In each one of these tubules we 

 distinguish the following segments : (i) Bowman's capsule, or the 

 ampulla, surrounding a spheric plexus of capillaries, the glomerulus, 

 which, with the capsule of Bowman, forms a Malpighian corpuscle ; 

 (2) a proximal convoluted portion ; (3) a U-shaped portion, con- 

 sisting of straight descending and ascending limbs and the loop 

 of Henle ; (4) a distal convoluted portion or intercalated portion ; 

 and (5) an arched collecting portion ; from the confluence of a num- 

 ber of these are formed the larger straight collecting tubules, which, 

 in turn, finally unite to form the papillary ducts or tubules of 

 Bellini, which pass through the renal papillae and empty into the 

 renal pelvis. Besides the uriniferous tubules the kidney con- 

 tains a complicated vascular system, a small amount of connective 

 tissue, etc. 



In a longitudinal median section the kidney is seen to be com- 

 posed of two substances, the one, the medullary substance, pos- 

 sessing relatively few blood capillaries and containing straight 

 collecting tubules and the loops of Henle ; the other, the cortical 

 substance, richer in blood-vessels, and containing principally the 

 Malpighian corpuscles and the proximal and distal convoluted tu- 

 bules. In each renal lobe we find these two substances distributed 

 as follows : The Malpighian pyramid consists entirely of medullary 

 substance, which sends out a large number of processes, the medul- 



