174 BIRDS. 



are also calculated for motion on the ground ; some families for 

 motion on the surface of the water, or even to a certain degree 

 through a mass of the same element ; and their structure is 

 varied to suit these different kinds of motion. 



The part of the spine in birds which corresponds to the back 

 is immoveable, and the only portions of the vertebral column 

 capable of motion are the vertebrae of the neck and those of 

 the tail. Their pectoral members or arms are elongated to 

 wings proper only for flight. These members or wings, composed 

 of one long finger and the vestiges of two others, are furnished 

 with long, stiff, but elastic feathers, disposed like a fan, which 

 follow the movement of the bone, and when extended occupy 

 a large surface. The wings are attached by a double clavicle, 

 and are supported by a broad sternum, carinated in front like 

 the keel of a ship. This sternum is formed of five pieces, 

 strongly joined together ; and the greater or less ossification 

 of these pieces is always relative to the powers of the bird for 

 flight. The long feathers, attached to what may be termed the 

 hand, generally to the number of ten, are termed primaries ; 

 the secondaries, variable in number, are those attached to the 

 fore-arm ; and scapulars are the smaller feathers which are at- 

 tached to the humerus. In describing birds the term remiges 

 is also used to denote the feathers of the wings which serve as 

 oars ; and rectrices those of the tail, which have been consider- 

 ed to act as a rudder. The smaller feathers which cover the 

 base of the wing and tail are termed tectrices. 



The anterior extremities, destined to support them in flight, 

 can neither be used for prehension nor support, and birds thus 

 take objects from the ground by their mouth. The neck is 

 elongated, and the body thrown forward, that the bill may easily 

 reach the ground. The pelvis is lengthened to furnish an at- 

 tachment for the muscles which support the trunk upon the 

 thighs ; and there is an arrangement of muscles going from the 

 pelvis to the toes, in such manner that the weight of the ani- 

 mal bends the toes, and enables it to sleep perched upon one 

 foot. 



The bony part of the tail is short, but it carries a row of 

 strong feathers which spreading contribute to support the bird. 

 The number of these feathers is generally twelve, sometimes 



