98 THE BOOK OF MIGRATORY BIRDS 



of quadrupeds; many of them also are very long lived. 

 The swan is said to attain the age of a hundred years. 



The organs of breathing in birds are admirably con- 

 structed for the purpose of enabling them to fly with 

 greater ease. The air passes through their lungs into air- 

 cells, which either surround or are joined to the heart and 

 liver, and other internal parts; there are even air-cells in 

 the bones, which are supplied in the same way. In the 

 Wild Swan (Cygnus ferus) the wind-pipe, after passing 

 down the long neck of the bird, is curiously coiled up 

 within the breast-bone for the same purpose. Naturalists 

 state that in the Tame Swan (Cygnus olor) the trachea does 

 not make this convolution. 



There is a closer resemblance than appears at first sight 

 between the wings of birds and the fore-legs of quadrupeds. 

 The joints are similar, and in both the upper part of the 

 limb consist of a single bone, and the lower of two. 



The brain in birds is larger in proportion than that of 

 quadrupeds. The eyes are so large that there is no brain 

 between them, but only a thin plate of the skull. The 

 organ of smell lies at the root of the beak. The tongue 

 in most birds is gristly, and not formed for any delicacy 

 of taste. In the parrot it is thick and fleshy, and also in 

 the duck and goose. They have no outward ear like 

 quadrupeds, but an opening covered with feathers. 



Birds of prey are known by their bent beak and crooked 

 talons, very powerful weapons, which they employ to take 

 other birds, and even weak quadrupeds and reptiles ; they 

 have all four toes; the nail of the hind toe and that of the 

 internal toe are the strongest. They form two families, 

 the diurnal and the nocturnal. The former have a quick 

 and piercing sight ; a membrane called the cere covers the 

 base of the beak, in which are placed the nostrils ; they 

 have three toes before and one behind ; the two outward 

 toes are almost always united at their base by a short 

 membrane; the plumage is close; the feathers are strong, 

 and the flight powerful. 



