AMPHIBIA. 487 



3. Amphibia. 



IN the small tribe denominated by Cuvier 

 Amphibia, and consisting of the Phoca, or Seal, 

 'and the Trichecus, or Walrus, we perceive that 

 an advance is made towards a fuller develope- 

 ment of the limbs : these animals having a 

 distinct neck and pelvis, and both hind and 

 fore extremities. In the seal the hind legs are 

 drawn out posteriorly to a considerable length, 

 and placed parallel to each other : when united 

 and alternately raised and depressed, they per- 

 form the same office as the tail of the cetacea, 

 and propel the animal forwards : but when em- 

 ployed separately, they are more qualified to act 

 as oars. The walrus has feet still more deve- 

 loped, and distinctly divided into toes, which are 

 disposed so as to strike backwards against the 

 water. 



4. Mammiferous Quadrupeds in general. 



FROM the imperfectly developed aquatic and 

 amphibious tribes we gradually ascend to the 

 more finished structures of mammiferous quad- 

 rupeds, which are expressly fitted for progression 

 on land. In these the powers of developement, 



