164 HUMAN PHYSIOLOGY. 



EXCRETION. 



The principal excrementitious fluids discharged from the body are 

 the urine, perspiration, and bile ; they hold in solution principles 

 of waste which are generated during the activity of the nutritive 

 process and are the ultimate forms to which the organic constituents 

 are reduced in the body. They also contain inorganic salts. 



The urinary apparatus consists of the kidneys, ureters, and 

 bladder. 



KIDNEYS. 



The kidneys are the organs for the secretion of urine ; they 

 resemble a bean in shape, are from four to five inches in length, 

 two in. breadth, and weigh from four to six ounces. 



They are situated in the lumbar region, one on each side of the 

 vertebral column behind the peritoneum, and extend from the 

 eleventh rib to the crest of the ilium ; the anterior surface is convex, 

 the posterior surface concave, the latter presenting a deep notch, 

 the hilus. 



The kidney is surrounded by thin, smooth membrane composed of 

 white fibrous and yellow elastic tissue ; though it is attached to the 

 surface of the kidney by minute processes of connective tissue, it 

 can be readily torn away. The substance of the kidney is dense, 

 but friable. 



Upon making a longitudinal section of the kidney it will be ob- 

 served that the hilus extends into the interior of the organ and ex- 

 pands to form a cavity known as the sinus. This cavity is occupied 

 by the upper, dilated portion of the ureter, the interior of which 

 forms the pelvis. The ureter subdivides into several portions, which 

 ultimately give origin to a number of smaller tubes, termed calyces, 

 which receive the apices of the pyramids. 



The parenchyma of the kidney consists of two portions viz. : 



1. An internal or medullary portion, consisting of a series of 

 pyramids or cones, some twelve or fifteen in number. They pre- 

 sent a distinctly striated appearance, a condition due to the 

 straight direction of the tubules and blood-vessels. 



2. An external or cortical portion, consisting of a delicate matrix 

 containing an immense number of tubules having a markedly con- 



