CHAPTER XXII. 



URINARY EXCRETION. 



The urine is the most important fluid excretion, for by it, in 

 mammalia, nearly all the nitrogen of the used-up proteid leaves 

 the body in the form of urea. The construction of the urinary 

 glands requires the special notice of the physiologist. 



FIG. 170. 



Section of Kidney of Man. a. Cortical substance composed chiefly of convoluted 

 tubules ; the portions between the medullary pyramids form the columns of Berlin (e). 

 b. Pyramids of msdullary substance, composed of straight tubes, etc., radiating toward 

 cortex, to form the pyramids of Ferreiu. d. Commencement of ureter leading from 

 central sack or pelvis, c. Papillae where the tubes open into pelvis. (Cadiat.) 



STRUCTURE OF THE KIDNEYS. 



The kidneys may be called complex tubular glands, because 

 the tubes of which they are composed are made up of a number of 



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