BIRDS. 115 



but a long, straight, pointed tusk implanted in the inter- 

 maxillary bone, and directed in the line of the body. 

 The developed tusk is on the left side ; an undeveloped 

 one exists on the right side. 



The Narwhal, M. monoceros, Linn., resembles a por- 

 poise except in its spirally furrowed tusk, sometimes ten 

 feet long. These animals inhabit the Arctic seas, and 

 are pursued and skilfully captured by the Esquimaux. 



Remains of extinct Cetacea occur in various parts 'of 

 North America, as well as in the Old World. The Zeu- 

 glodon was a Cetacean seventy feet long, whose remains 

 abound in the Southern States, especially in Alabama. 



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 



