388 



STRUCTURE OF THE TUBULES. 



112) connects the latter with one of the straight coUecting tubes (13) of a medullary ray. As 

 torifiZ^tohvroceeto through the boundary zone it receives numerous junctional 

 [uU and when it reacLs the boundary zone, it forms one of the collecting tubes (fig. 243, 0), 



Sub-capsular layer without Mal- 

 pighian corpuscles. 



12. First part of collecting tube. 

 11. Distal convoluted tubule. 

 V A. CORTEX. 

 10. Irregular tubule. 



3. Proximal convoluted tubule. 

 J). Wavy part of ascending limb. 

 2. Constriction or neck. 



4. Spiral tubule. 



4. Spiral tube. 

 13. Straipht part of collect 



Inner stratum of cortex 

 without Malphigian _J 

 corpuscles. 



1. Malpighian tuft surrounded 

 by Bowman's capsule. 



?. Spiral part of ascending limb 

 of Henle's loop. 



B. BOUNDARY ZONE. 



5. Descending limb of Henle's 

 loop-tube. 



7 & 8. Ascendine limb of 

 Henle's loop-tube. 



(J. Henle's loop, 



C. PAPILLARY ZONE. 



Fig. 242. 

 Diagram of the course of two uriniferous tubules {Klein and Noble- Smith). 



which unite with one another at acute angles to form the larger straight excretory tubes or 

 ducts of Bellini (15), which open on the summit of the Malpighian pyramids into a calyx of the 

 i>elvis of the kidney. In the cortex the collecting tubules are 45 /x in diameter, but where they 

 have formed an excretory tube (0), their diameter is 200 to 300 fi ; 24 to 80 of these tubes open 

 on the apex of each of the 12 to 15 Malpighian pyramids. In the lowest and broadest part, the 

 membrana propria is strengthened by the presence of a thick supporting framework of con- 

 nective-tissue. 



Structure of the Tubules. [Below the neck, the tubules are lined everywhere by a single 

 layer of nucleated epithelium.] Bowman's capsule, which is about ^ inch in diameter (fig. 

 244, II), consists of a homogeneous basement membrane lined internally by a single continuous 

 layer of flattened cells (k). According to Roth, the basement membrane itself is composed of 

 endothelial cells. [In the foetus the lining cells are more polyhedral.] "Within the capsule 

 lies the glomerulus or tuft of blood-vessels. The cells lining the capsule are reflected over and 

 between the lobules of which the glomerulus consists. The glomerulus may not completely fill 

 the capsule, so that, according to the activity of the kidney, there may be a larger or smaller 



