BIRDS. IIS 



which not only unites the 

 toes, but extends far beyond 

 the nails ; in the hind feet 

 the membrane terminates 

 at the root of the nails, and 

 the tail is flat. The whole 

 body is covered with short, 

 brown fur. These animals 

 live in ponds and quiet 

 streams, and dig burrows 

 in the banks, in which they 



rear their young. Only one or two species are known. 



They are less than two feet in length. 



SECTION II. 



THE CLASS OF BIRDS. 



THE Class of Birds comprises all oviparous vertebrates 

 which are clothed with feathers, furnished with a .bill, 

 and organized for flight. They have warm blood, and 

 a complete double circulation. They are all bipeds ; the 

 body is inclined before their feet, the thighs are directed 

 forward, and the toes elongated, forming a broad sup- 

 porting base. The head and neck are more or less pro- 

 longed, the latter very flexible, and generally containing 

 twelve or more vertebrae. The length of the neck and 

 its great flexibility enable these animals to touch every 

 part of the body with the bill. The trunk, serving as a 

 point of support for the extended locomotive members, 

 has little flexibility, the vertebrae of this portion being 

 more or less firmly joined together. The pelvis is much 

 lengthened to furnish points of attachment for the muscles 

 of the thighs ; and the sternum is of great extent, to bear 

 the extensive muscles for moving the wings in flight. 

 The sternal as well as the vertebral parts of the ribs are 



