82 ZOOLOGY. 



constituted by that portion of the tubes which is massed 

 into heaps rolled on each other; the other part is called 

 tubular or medullary, being the part formed by the fasci- 

 culi themselves. In the young, and in many animals, 

 throughout life, such as the bear and otter, these pyramids 

 remain distinct, and each kidney is then composed of several 

 separate lobes; but generally they unite together, and the 

 calices, which are but excrementory tubes, unite to form 

 a pelvis or general reservoir, from which proceeds the 

 ureter (Fig. 52 d). A great number of bloodvessels creep 

 between these secreting tubes, and constitute, in the cortical 

 portion of the gland, a very close network, in the midst of 

 which may be seen certain spherical bodies, formed also of 

 bloodvessels collected into bunches in the interior of the 

 ampulla already mentioned. 



The urine is formed in the cortical part of the kidneys. 

 It descends by the tubular part into the calices, and thence 

 into the pelvis of the kidney ; this terminates in the ureter 

 (Fig. 53 b), by which the urine descends to the bladder. This 

 latter organ is situated in the pelvis and behind the os pubis. 

 It is formed internally by a mucous membrane ; externally, 

 fry a muscular and cellular layer. The peritoneum also par- 

 tially invests it, and gives it support. Interiorly it terminates 

 in the canal of the urethra, by which the urine escapes from 

 the body. 



163. The urine is a yellowish acid liquid, which in 

 man, in the normal state, is composed of 93 parts water, 

 3 of a peculiar substance called urea; a very small portion 

 of uric acid, lactic acid, various salts, as muriate of soda, 

 alkaline sulphates, phosphate of lime, &c., make up the 100 

 parts. 



In carnivorous mammals the urine resembles that of man, 

 but the uric acid is wanting. In herbivorous mammals the 

 urine is alkaline, and a peculiar substance is found, the hip- 

 puric acid, as well as many earthy carbonates. In many 

 birds, and in most reptiles, the urine is composed mostly of 

 uric acid; whilst in frogs and tortoises (turtles and tortoises) 

 it contains urea and albumen. Its composition in fishes 

 appears to be the same ; but in insects we again find uric acid. 

 Disease affects its composition in man. 



164. The extreme rapidity with which various drinks, 

 medicated or simple, pass from the stomach to the bladder, 

 and so escape externally by the urethra, is well known ; yet 



