250 



HISTOLOGY. 



grow out. Each tubule has an enlarged extremity (Fig. 280) which divides 

 into two branches with a U-shaped crotch, like a tuning-fork. The 



CORTEX 



_ _ Pars Radiata 

 -ParsConvoluta 



- r V - -^ A- Pyramid 

 ^"-A (Medulla! 



'.-'T~r.-r Papilla 

 l/^v-'^-f -^TJ/ Renal Column 



d - 



FIG. 280. RECONSTRUC- FlG - 281. CROSS SECTION OP AN ADULT KIDNEY. 



' TION OP THE URETER. (With modifications, after Brodel.) 



RENAL PELVIS, AND 

 ITS BRANCHES IN A 20 

 MM. HUMAN EMBRYO. 

 (Huber, Amer. Jour- 

 nal of Anat., Suppl. 

 to vol. iv). 



branches subdivide repeatedly in the same manner, so as to make pyram- 

 idal masses of straight tubules radiating from the calyces. From 2 to 9 

 primary pyramids are said to fuse to form a macroscopic pyramid of the 



adult kidney (Fig. 281). The 

 nipple-like apex of the pyramid 

 projects into the renal calyx form- 

 ing a renal papilla. Each pa- 

 pilla is covered by the pelvic epi- 

 thelium, which is continuous 

 with that which lines the collect- 

 ing tubules. The trunks of these 

 tubules near the papilla are called 

 papillary ducts and their outlets 

 are named foramina. Each pa- 

 pilla has from 15 to 20 foramina. 

 Sometimes two papillae project 

 into one calyx. 



The renal pyramids consti- 

 tute the medulla of the kidney. 



Except toward their apices they are surrounded by cortical substance. The 

 cortex forms the peripheral part of the kidney, and it also dips down be- 

 tween the pyramids almost to the pelvis. In this way the cortex forms 



FIG. 282. FROM A SECTION OF A KIDNEY OP AN 18 

 MM. HUMAN EMBRYO. X 233. (Huber, Amer. 

 Journal of Anat., Suppl. to vol. iv.) 



a., Primary collecting tubule, with dilated extremity; 

 b, b'., inner layer, and c., outer layer of dense mes- 

 enchyma; d'., loose mesenchyma; e., vesicle, the 

 beginning of a renal tubule. 



