XIL] THE EXCRETORY ORGAXS. 483 



imbedded in the depressions of the under surface of the 

 sacrum, which is so expanded in the entire class Aves. 



A condition of the kidneys analogous to that which at an 

 early period exists in man, may not only persist throughout life 

 in other animals, but may be much more complete, as in the 

 Seals and Cetacea, where the kidneys are so divided into small 

 lobes as to resemble a bunch of grapes. As many as 200 

 lobes have been counted in the Dolphin's kidney. 



11. Two small glandular bodies, of unknown function, 

 called SUPRA-RENAL CAPSULES, are placed one on the 

 summit of each kidney. Each capsule is a flattened, tri- 

 angular body, and shaped something like a cocked hat. It 

 is formed of cellular tissue, often mixed with much fat, and 

 provided with a fibrous coat which sends processes into the 

 interior of the gland, these processes accompanying blood- 

 vessels and nerves, which are numerous. 



These organs exist in all the members of man's class, and 

 in a general way resemble his in position and form. They 

 are relatively largest in Rodents, as in the Coypu and Por- 

 cupine, where they are cylindrical in form. 



They are relatively smallest in the Cetacea amongst Mam- 

 mals, where, as also in Seals, they exhibit a lobulated exterior 

 like that of the kidney itself. 



In Birds these organs are relatively smaller, being in the 

 Goose only about the size of a pea. They also vary more 

 in shape in Birds than in man's class, and sometimes become 

 confluent. They are usually, in Birds, placed on the inner 

 side of the kidneys. 



The supra-renal capsules may be in the form of a single, elon- 

 gated, narrow, lobulated body, situate behind the renal organ, 

 as mostly in Sharks ; or may appear as a yellow streak on the 

 ventral aspect of the urinary gland, as in the Frog and Toad. 



Each supra-renal capsule may be divided into a greater or 

 less number of lobules, as in some Urodeles, the Sturgeon, 

 and many Fishes. 



12. The SPLEEN of man has been noticed in the Fifth 

 Lesson of " Elementary Physiology," 28. It is a ductless 

 body, of irregular and variable shape, richly supplied with 

 blood-vessels, and lying beneath the diaphragm at the car- 

 diac end of the stomach. 



In the possession of a spleen man agrees with all other 

 Vertebrata, with the exception of the Lancelet, and possibly 

 also with the exception of the Marsipobranchii, Lepidosiren^ 

 and Ceratodus. 



