CLASS AVES. 97 



aquatic life, is nevertheless strictly an air-breather ; and 

 the breathing-organs are in the form of spongy lungs 

 placed within the cavity of the chest. The air, also, is 

 admitted from the lungs to a nmnber of air recej)tacles or 

 chambers placed in diflerent parts of the body. Further, 

 the air is admitted to the interior of a considerable 

 number of the bones, which are hollow, and filled with 

 air in place of marrow. By means of these arrange- 

 ments, the body of the animal is considerably lightened, 

 and the blood is likewise more completely exposed to 

 the action of the air than could otherwise have been 

 the case. 



The nervous system consists mainly of a brain, pro- 

 tected within the skull, and a spinal marrow, protected 

 within the backbone. 



The peculiarities of the skeleton of the Goose are so 

 numerous that nothing can be done here beyond mei'ely 

 pointing out one or two of the more important ones. One 

 of the most striking of these is the form of the breast- 

 bone, which has the shape of a broad plate carrying a 

 great central ridge or keel of bone. The object of this 

 is to offer a greatly extended surface for the attachment 

 of the very powerful muscles required for the movement 

 of the wings. Again, the neck is very long and flex- 

 ible, and is composed of a number of joints, so as to 

 allow the bird to apply its bill to all parts of the body ; 

 an arrangement rendered necessaiy by the fact that 

 the limbs cannot be used in grasping or laying hold of 

 objects. The last joint of the tail, again, is a large plough- 

 share-shaped bone, whirh is set on nearly at right angles 

 to the rest of the backbone, and which serves for the 

 elevation and depression of the feathers of the tail. 

 Finally, the skull is united with the backbone by a 

 single joint or pivot. 



Lastly, the Geese, like all other birds, produce their 

 young in the form of eggs, and, like most birds, sit upon 

 these eggs so as to hatch them by the warmth of their 

 own bodies. When hatched, the young birds are quite 

 active and can run about and look for food, whilst their 



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