184 



1NTEODUCTOEY CHAPTEE. 



The length and flexibility of the neck enable the bird to make the 

 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 



Fig. 48. 



the feathers ; when long, they are stretched out beneath or behind 

 the tail, which is more or less expanded, and helps to support 

 the body in the air, as well as, by acting in the manner of a 



Fig. 49. 



rudder, to change its direction, or, by being expanded, to break 

 its descent." 



The wings of birds are acute or obtuse. The more angular the 



Fig. 50. 



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, one for each vertebra, which 

 are capable of depressing and elevating the tail in various degrees ; 

 while a series of connections, whose fibres invest the base of the 



