76 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 nth 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 a 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 observed 

 that the hilus extends into the interior of the organ and expands 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 Q\ medullary portion, consisting of a series of pyramids 

 or cones, some twelve or fifteen in number. They present a distinctly stri- 

 ated 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 con- 

 taining an immense number of tubules having a markedly convoluted 

 appearance. Throughout its structure are found numerous small ovoid 

 bodies -termed Malpighian corpuscles. 



