ORNITHOLOGY. 275 



flight, and the bird depends principally on its bill for gathering 

 its food, it became necessary, as the bones of the back have 

 scarcely any motion, that the neck should be as it is, long and 

 flexible. Hence, while in the mammals, the vertebras of the 

 neck are seven, there being no more even in the Camelopard, 

 the deficiency of motion in the back is made up in birds by an 

 increase in the vertebrse of the neck, (B.) proportioned to their 

 wants Thus the Raven has twelve neck bones, the Domestic 

 Cock thirteen, the Ostrich eighteen, the Stork nineteen, and the 

 Swan twenty-three, which is the largest number yet ascertained, 

 while the smallest is ten. These are so joined together, that the 

 head can be turned completely around, (the position which the 

 bird takes when at rest,) or moved in any direction, so that the 

 bird can touch every point of its body with its bill. 



The trunk is sustained on the thighs by very powerful mus 

 cles ; another set of which passes from the lower part of the 

 thighs to the toes, turning over the knee and heel, in such a 

 way that the flexion or bending of these joints shall shorten them. 

 Hence, the simple weight of the body flexes the toes, so that birds 

 are enabled to sleep perched on one foot. But the pectoral mus 

 cles, as a general rule, show the greatest development. The 

 breas* bone, or sternum, is made to project forwards with an ele 

 vated ridge or keel. To this, the powerful muscles which 

 depress the wings, are attached, The depth of the keel is a partial 

 criterion as to the power of flight ; in the Harrier it is deep; in 

 the Ostrich, where the wings are not sufficiently developed to 

 raise the bird from the ground, it is quite flut. 



The jaws of the bird are not furnished with teeth, but the 

 place of these organs is supplied by a casing of horn, termina 

 ting; in a point at the tip, and brought to an edge on the side of 

 the jaw. This horny casing is known as the beak or bill ; the 

 name mandibles is given to the upper and lower divisions. In 

 Birds of Prey, \see Plate of Birds Beaks and Heads,) the beak 

 is like a carving or dissecting knife ; in the Woodpeckers it is an 

 effective chisel ; in the Snipe and Woodcock, it is a long and 

 slender probe, furnished at the tip with copious nerves of sensa 

 tion for feeling in the deep earth of bogs and marshes ; in the 

 Parrots, it is a climbing hook, or a fruit knife; in the Swallows 

 and Goat Suckers, it is a fly-trap; in the Swans, Geese and 

 Ducks, it is a flattened strainer, with nerves on the inside for the 

 detection of the food remaining after that particular operation 

 which almost every one must have observed a duck perform in 

 muddy water ; in the Storks and Herons, it is like a fish-spear ; 

 in the Cross-Bills, or Seed-eating Birds, it forms a pair of Seed- 



12 



