2 . ,, ( , , .UWARY ORGANS. 



the chyle; this fluid receives the products of the metamorpho- 

 sis of the tissues, and having carefully examined its chemical 

 composition, we endeavoured to point out the changes which 

 the blood undergoes in its circulation through the lungs, the 

 liver, and some other glandular organs. The lungs were 

 shown to be materially concerned in the excretion of car- 

 bonic acid and water, (besides ammonia). The liver, besides 

 fulfilling certain other functions, we found to be an excretor 

 of hydrocarbons, in which function it is aided by the skin. 

 We have now to consider a system of organs destined to 

 remove from the system the superfluous water and nitro- 

 genous and saline constituents of the blood. 



The urinary system in its most differentiated and perfect 

 form, consists of (a), the kidneys, two in number, whose 

 function it is to form the urinary secretion ; (6), the ureters, 

 which are canals leading from the kidneys to a reservoir for 

 the secretion, viz., (c), the urinary bladder, where the urine 

 accumulates, and from which it is at intervals discharged 

 through (d) the urethra. 



The kidneys are two glandular organs, situated at the back 

 part of the abdomen, in each lumbar region. They are im- 

 bedded in fat, and their inferior surface is covered by the 

 superior surface of the peritoneum. The shape of the kid- 

 neys is so peculiar, that objects are often spoken of as kid- 

 n'ey-shaped, or reniform, when resembling the kidneys in 

 form. 



A kidney presents slightly convex inferior and superior 

 surfaces ; an external extremely convex border, and an inter- 

 nal concave border. In this concavity or notch, the ureter, 

 the large vein and artery of the kidney, and the nerves 

 and lymphatics, are inserted; it is called the hilus of the 

 kidney. The surface of the kidney is covered by a fibrous 

 capsule, which can be easily separated from the glandular 



