i88 



ELEMENTS OF BIOLOGY 



fishes, Amphibia, reptiles, and birds, is a common receptacle for the 

 contents of the colon and for the wastes from the excretory organs, 

 is separated in the higher mammals into urinary and rectal organs. 

 The Human Kidney. The chief organ of excretion in Man 

 and other mammals is the kidney (Fig. 131). In the human body a 

 pair of these are located closely associated with the dorsal wall of 

 the peritoneal cavity on either side of the mid-line. The human 

 kidney is composed of two regions, an outer, known as the cortex, 

 and an inner region, the medulla. The cortex contains great num- 



CORTEX 



ffFNAL PAPILLA 



RENAL PELVIS 



URETER 



Fig. 131. — The gross anatomy of the human kidney in diagrammatic section. 

 (After Sobotta: Atlas and Texthool{ of Human Anatomy, published by W. B. 

 Saunders Co.) 



bers of excretory units, each of which consists of a small structure 

 shaped much like a champagne glass, termed the glomerulus (Fig. 

 132). Within the hollow of the glomerulus is a small artery and a 

 small vein. The stem of the glomerulus consists of a duct; a short 

 distance from the glomerulus the duct is thrown into convolutions 

 and the walls of this convoluted portion also receive an artery and a 

 vein. The nitrogenous wastes of metabolism diffuse out from the 

 body cells into the lymph and blood stream. In the liver they are 

 converted into urea. In the glomerulus of the kidney this sub- 

 stance, together with other waste materials, is filtered out of the 



