390 PRACTICAL ANATOMY. 



defined to be a collection of cones or pyramids already 

 described, and invested by delicate fibrous tissue. 



The renal arteries enter the hilum and break up into 

 a number of branches, which penetrate the columns of 

 Bertin and reach the bases of the pyramids, over which 

 they form anastomotic arches. From these are given 

 off two sets of branches, the medullary (arteriolae rectae) 

 and the cortical. The former supply the pyramids ; the 

 latter pass outward toward the periphery and send off 

 numbers of capillary branches, which are very delicate 

 and terminate in a spheroidal tuft of anastomosing capil- 

 laries located within the Malpighian capsule. The for- 

 mation of the capsule is not fully understood, but it is 

 supposed to be made by invagination, the tuft of capil- 

 laries resting within the capsule invested by the lining 

 cells. Some believe it to hang free in the capsule ; others 

 claim that the tuft distends the capsule, but is shut out 

 from the tubule by a partition layer of cells. The 

 venous capillaries leave the corpuscle and follow the 

 course of the arteries. 



THE URETER. 



The ureter or duct of the kidney runs from the pelvis 

 of the kidney to the bladder. It is about seventeen 

 inches long, half as thick as a lead-pencil, and is com- 

 posed of three coats, a fibrous, a muscular, and a 

 mucous. The fibrous coat is continuous with the cap- 

 sule of Bowman and is lost on the bladder. The mus- 

 cular coat is formed by longitudinal and circular fibres, 

 which become thinner toward the bladder. The mucous 

 coat is formed of columnar epithelium in different stages 

 of development, resting on a basement membrane. The 

 mucous membrane is thrown into slight longitudinal 

 folds. The upper, expanded part of the ureter forms 

 the pelvis of the kidney. It dips into the infundibula 



