A STUDY OF THE SKIN AND THE KIDNEYS 249 



M 



RV 



kidney described above, and the apex of each pyramid 

 projects like a papilla into the pelvis or enlargement of the 

 ureter (Fig. 113). 



Microscopical Structure. The kidney is composed of an 

 enormous number of complicated tubules that begin in 

 the cortical region, pass 

 through the medullary 

 layer (giving the appear- 

 ance of fine lines through 

 the pyramids referred to at 

 above), and finally open 

 on the summits of the 

 pyramids into the cavity 

 of the organ. At the 

 beginning of each tubule 

 is a tiny spherical swell- 

 ing richly supplied with 

 a network of blood vessels 

 (Fig. 114). Here it is 

 probable that water oozes 

 out of the blood and passes 

 thence through the tortu- 

 ous course of the tubule. 

 The latter also is sur- 

 rounded with blood capil- 

 laries. Urea, salts, and 

 other waste matters are 

 without doubt taken out of the blood and lymph by the cells 

 in this region of the tube, and the urine thus formed passes 

 through the winding course of the ducts until it finally oozes 

 out into the cavity (pelvis) inclosed by the medullary layer. 



Course taken by the Urine. The urine is therefore secreted, 

 to a large extent at least, in the cortex of the kidney, and 

 thence passes through the pyramids of the medullary layer 

 into the pelvis of the organ. From this cavity in each kid- 

 ney the ureter conducts the liquid to a storage sac called the 



FIG. 113. Section of Human Kidney. 



Ct = cortex. 



M = medulla. 



P = pelvis of kidney. 

 Py = pyramids in medulla. 

 RA = renal artery to kidney. 

 RV= renal vein to kidney. 



U= ureter. 



