366 



EXCKETION 



Corns. — When the skin on the feet or the hands is nibbed, 

 the parts protect themselves by increased development of the 

 epidermis and thus form horny spots or callouses. Sometimes, 



Fig. 167 — Section of a com. Note the thickened epidermis over one papilla, and 

 the manner in which' it presses into the sensitive dermis below. Overton, 

 Applied Physiology. 



on the feet, these spots grow inward, and a point of hardened cells 

 forms which presses inward into the sensitive dermis. The re- 

 sult is a painful formation called a corn. 



Othek Escretoey Organs. 



The urinary organs. — On each side of the backbone, in 

 the part of the abdominal cavity a Uttle below the lower 

 ribs, lie two bean-shaped bodies about four inches long, two 

 inches wide, and one inch thick. These two organs 

 are the kidneys. They are embedded in a thick layer of 

 fat, and from the curved-in portion of each emerges a tube 

 called the ureter. These ureters are continued downward 

 and enter a baglike body covered externally with muscle 

 and lined with mucous membrane. This body is the blad- 



