53 



The lesser pectorals are situated beneath the great pectoral, and arise 

 from the base of the crest of the sternum ; they pass upwards, and the tendon 

 by passing through the interspace between the clavicle, coracoid scapula, has the 

 direction of its force altered, and being inserted on the upper part of the 

 humerus, serves as an elevator of the wing. 



This is a peculiarly beautiful contrivance, as it enables the mass of the 

 muscle to be kept low, and thereby the centre of gravity also — a point of great 

 importance in flight — and it also provides for the raising of the wing. 



It is evident that the muscles used for raising the wing need not be so 

 strong as those employed in depressing it ; for in the up stroke the wing is always 

 drawn in and the feathers overlap one another, so that a comparatively small 

 surface is presented to the resistance of the air. They must, however be capable 

 of intensely rapid action, as the up stroke must be repeated as often as the down 

 stroke, and in some birds this is very many times in a second. The other muscles 

 of the wing are the extensors and flexors of the fore arm and the fingers, by means 

 of which they are enabled to stretch out or draw in the wiug. 



With this brief review of the muscles of the wings, I will pass on to 

 notice the feathers. Birds are the only animals furnished with feathers, and no 

 covering could possibly be imagined which combined the needful qualities of 

 warmth, firmness, flexibility, lightness, and I may add beauty, more admirably 

 than feathers. A feather is composed of a quill which is prolonged into a shaft 

 which runs the whole length of the feather, and from each side of the shaft 

 proceed branches ; these branches are set on obliquely and point toward the end 

 of the feather ; from each of the branches fine rays set very close together 

 proceed, and on the side next to the shaft, small hairs turned so as to form hooks 

 overlap the rays of the next branch and hold it firmly together. It is these 

 minute booklets which give the appearance of the vane of a feather sticking 

 together when it is attempted to separate it. The whole feather is composed 

 of a horny substance and is not vascular after the growth has taken place. It 

 must be carefully noticed that the wing feathers have the shaft placed not in the 

 middle of the vane, but considerably to the front, so that the stiff portion of the 

 feather is presented to the wind and the more flexible part is behind : the object 

 of this I will notice in the next section. 



The feathers of the wing are divided into primaries and secondaries : the 

 primary feathers are much the longest and stiffest, and are the chief instruments 

 in flight ; they are situated on the fingers and hand or carpus ; the secondaries 

 are situated on the fore arm ; they are much more numerous and also much more 

 irregular in nximber than the primaries; they are also more flexible. The 

 primary feathers are important aids in classification. 



Sectiok III. 



Having now taken a brief view of those points in the structure of birds 

 which are peculiarly modified for the purpose of flight, and also having noticed 



