CHAPTER XIII. 

 THE URINARY ORGANS. 



THE action of the urinary organs is excretory, serving to 

 remove from the blood waste katabolic products and super- 

 fluous ingested substances. The urinary apparatus consists 

 of the kidneys, ureters, bladder, and urethra, the latter in the 

 male being also utilized in the genital function. 



The Kidneys. 



General structure : The kidneys are compound tubular 

 glands. They exhibit two parts, the parenchyma or secreting 

 portion, and the sinus, a cavity containing the calices of the 

 ureter in which the urine collects and is discharged into the 

 ureter, which is the outlet-duct of the kidney. The sinus is 

 situated within the kidney, of which the concave inner mar- 

 gin constitutes the hilum of the organ, where the ureter, renal 

 artery, vein, lymphatics, and nerves enter. The renal paren- 

 chyma is arranged in a radiating manner about the sinus, and 

 consists of two well-marked zones, an outer or cortex, and an 

 inner or medulla. 



The structural elements of the kidney are the uriniferotis 

 tubules (beginning with prominent rounded bodies, the Mal- 

 pighian bodies), bloodvessels, and sustentacular connective 

 tissue, besides inconspicuous lymphatics and nerves and the 

 lining of the sinus. The kidneys, being derived from the 

 foetal Wolffian body, are developed from the mesoblast, thus 

 forming a notable exception to the usual epiblastic origin of 

 epithelium. 



The medulla of the kidney is composed of a number (eight 

 to eighteen) of conical bodies, called the pyramids of Mal- 

 pighi. These radiate about and from the renal sinus, with 

 their bases outward, resting against the cortex, and their 

 apices pointing in toward the renal pelvis (of the ureter), 



158 



