STRUCTURE OF THE KIDNEY. 



387 



Cortex. 



portion. According to Klein, the relative proportions of these three parts are cortex, 3*5 ; 

 boundary layer, 2 '5 ; and papillary portion, 4. The cortex has a light brown colour, and when 

 torn presents a slightly granular aspect, with radiating lines running at regular distances. The 

 granules are due to the presence of the Malpighian corpuscles, and the striae to the medullary 

 rays. The boundary zone is darker, and often purplish in colour. It is striated with clear and 

 red lines alternating with opaque ones, the former being blood-vessels and the latter uriniferous 

 tubules. The papillary zone is nearly white and uniformly striated, the strise converging to 

 the apex of the pyramid. The medulla is 

 much denser and less friable than the cortex, 

 owing to the presence of a large amount of 

 connective-tissue between the tubules. The 

 bundles of straight tubes of the medulla may 

 be traced at regular intervals running out- 

 wards into the cortex, constituting medullary 

 rays, which become smaller as they pass out- 

 wards in the cortical zone, so that they are 

 conical and form the pyramids of Ferrein 

 (fig. 241, PF). The portion of the cortex 

 lying between the medullary rays is known as 

 the labyrinth, from the complicated arrange- 

 ment of its tubules.] 



[Size, Weight. The adult kidney is about 

 11 centimetres (4*4 inches) in length, 5 centi- 

 metres (2 inches) wide, and 3 centimetres 

 (1 inch) in thickness. It weighs in the 

 male 113 "5 to 170 grms. (4 to 6 oz.), in the 

 female 113 '5 to 156 grms. (4 to h\ oz.). The 

 width of the cortex is usually 5 to 6 milli- 

 metres (i to \ inch).] 



I. The uriniferous tubules all arise within 

 the labyrinth of the cortex by means of a 

 globular enlargement, 200 to 300 fj. [y^ to 

 yts inch] in diameter, called Bowman's 

 capsule (tigs. 242, 243). After pursuing a 

 complicated course, altering their direction, 

 diameter, and structure, and being joined by 

 other tubules, they ultimately form large 

 collecting tubes, which terminate by minute 

 apertures, visible with the aid of a hand-lens, 

 on the apices of the papillae projecting into 

 the calices of the kidney 



Papillary 

 zone. 



Fig. 241 

 Each urinary tubule Longitudinal section of a Malpighian pyramid. 



PF, pyramids of Ferrein ; RA, branch of renal 

 artery ; RV, lumen of a renal vein receiving an 

 interlobular vein ; VR, vasa recta ; PA, apex 

 of a renal papilla : b, b, embrace the bases of the 

 renal lobules. 



is composed of a homogeneous membrana 



propria, lined by epithelial cells, so as to 



leave a lumen for the passage of the urine 



from the Malpighian corpuscles to the pelvis 



of the kidney. The diameter and direction 



of the tubules vary, and the epithelium differs 



in its characters at different parts of the tube, while the lumen also undergoes alterations in its 



diameter. 



Course and Structure of the Tubules. In the labyrinth of the cortex, tubules arise in the 

 spherical enlargement known as Bowman's capsule (fig. 242, 1), which invests (in the manner 

 presently to be described) the tuft of capillary blood-vessels called a glomerulus or Malpighian 

 corpuscle. By means of a short and narrow neck (2) the capsule becomes continuous with a 

 convoluted tubule, X in fig. 243. This tubule is of considerable length, forming many wind- 

 ings in the cortex (fig. 242, 3); the first part of it is 45 /u. wide, constituting the proximal or 

 iirst convoluted tubule. It becomes continuous with a spiral tubule of Schachowa (4), which 

 lies in a medullary ray where it pursues a slightly wavy or spiral course. On the boundary 

 line between the cortical and boundary zone, the spiral tubule suddenly becomes smaller and 

 passes into the descending portion of Henle's loop (5), which is 14 /j. in breadth, and is con- 

 tinued downwards through the boundary zone into the medulla, where it forms the narrow 

 loop of Henle (6), which runs backwards in the medullary part to the boundary zone. Here 

 it becomes wider (20-26 /*), and as it continues its undulating course, it enters a medullary ray, 

 where it constitutes the ascending looped tube (7), which becomes narrower in the cortex. 

 Leaving the medullary ray again, it passes into the labyrinth, where it forms a tube with 

 irregular angular outlines the irregular tubule (10), which is continuous with (fig. 243, n, n) 

 the second or distal convoluted tubule (11), which resembles the proximal tubule of the same 

 name. Its diameter is 40 /*. A short, narrow, wavy junctional or curved collecting tubule 



