ANATOMY OF BIRDS. 169 
ligible. Their bodies are oval, with the more powerful muscles 
placed on the breast, so that, when the horizontal position is 
assumed, the centre of gravity comes between the wings, and is 
kept near the lower part by the weight of the pectoral muscles. 
The length and flexibility of the neck enable the bird to make the 
Fig. 46.—Wing of Penguin. 
necessary changes in the centre of gravity, while the solidity of 
the dorsal spine gives advantage to the action of the muscles. 
The head is terminated by a pointed bill, which aids in cleaving 
the air; the feet, when short, are drawn up and concealed under 
the feathers ; when long, they are stretched out beneath or behind 
the tail, which is more or less expanded, and helps to support 
Fig. 47.—Wing of Kamichi or Crested Screamer. 
the body in the air, as well as, by acting in the manner of a 
rudder, to change its direction, or, by being expanded, to break 
its descent.” 
The wings of Birds (Figs. 45, 46, 47) are acute or obtuse. The 
more angular the wing of birds—that is to say, the longer the feathers 
~on the edge of the wing—the more rapidly does it propel itself 
through the air. The tail consists of a number of feathers, to which 
are attached a series of small muscles, which are capable of depress- 
G * 
