4i6 



COMPARATIVE ANATOMY 



with a slit-like aperture, the hilum. The kidneys are held in position 

 ])oth by the peritoneum and by a connective tissue renal fascia. Only 

 upper (anterior) and lower (posterior) surfaces of the kidneys are covered 

 with peritoneum, the middle of the right kidney being crossed by the 

 colon, that of the left by the pancreas. These relations, however, are 

 subject to considerable variation. 



Structiire. A cross section of the human kidney in the region of the 

 hilum shows that under its peritoneal and fatty investments the kidney 



PROXIMAL CONVOLUTED TUBULE, 

 DISTAL CONVOLUTED TUBULE, 



ARCUATE ARTERY- 

 ARCUATE VEIN 



COLLECTING TUBULE -rrrt-r 

 HENLE's LOOP-^j) 



COLLECTING TUBULE PAPILLARY DUCT 



EXCRETORY TUBULE 



CALYX— T • 



Fig. 341. — A diagram of the finer structure of a kidney. ^ is a section of the entire 

 kidney showing the contrast between cortical and medullary regions. The relations 

 of the chief arteries and veins are indicated. 5 is a reconstruction of a single tubule, 

 showing its relations to the blood and the pelvis of the kidney. (Reproduced in modified 

 form from "The Human Body" by Dr. Logan Clendening, (Copyright 1927, 1930 by 

 Alfred A. Knopf, Inc.) by permission of and special arrangement with Alfred A. Knopf, 

 Inc., authorized publishers.) 



is covered with a thin but tough fibrous capsule, which in a young kidney 

 may be pulled off like the skin of an orange. 



The substance of a kidney consists of an outer cortex and an inner 

 medulla. A variable number, three to twenty, of renal pyramids form 

 the medulla. Straus has shown that among Primates man and the 

 spider monkey are peculiar in having a multipyramidal kidney, while 

 the anthropoid apes have monopyramidal kidneys. Each pyramid has its 

 base upon the cortex, and a cone-shaped apex which projects as a papilla 

 into the renal sinus. The cortex, which is about half an inch thick, 

 appears striated from the presence of cortical rays. Between the renal 

 pyramids, the cortex extends to the renal sinus in the form of renal col- 

 umns in which blood is conveyed to and from the cortex. The renal 

 sinus is filled by the expanded termination of the ureter, the pelvis. 



