8 STRUCTURE OF THE WING. 



There seems, indeed, to be a very marked analogy between the feathers of birds and the 

 tusks or horns of many mammals. Both depend greatly on the sex and age of the 

 animal to which they belong, and their shape and dimensions are unfailing indications of 

 the vigour or feebleness of their owners. 



The expanse of the outstretched wings of every flying bird is so very great in comparison 

 with the size of the body, that there is need of very great muscular development in order 

 to give the powerful strokes by which the body of a bird is urged through the atmosphere. 

 It is for this purpose that the breast bone is furnished with the deep keel which has 

 already been mentioned, for its projecting edge and sides afford attachment to muscles of 

 enormous size, which are devoted to the purpose of drawing the wing forcibly downwards. 

 Although in the gallinaceous birds, of which the common barn-door fowl is a familiar 

 example, the pectoral muscle, as it is called, is not so largely developed as in many of the 

 swift-winged birds, it attains to considerable dimensions, as may be seen by every one in 

 carving a common fowl, whether it be boiled or roasted. This muscle forms the solid 

 and delicately flavoured meat which is attached to the wing when removed, and also 

 constitutes the greater part of the " breast." 



Strength, however, is not the only requisite in a bird's wing. It is evident that if the 

 stroke were only made upwards and downwards, the bird would never rise in the air, 

 much less make any progress forwards. On gently moving the wing of a dead bird, we 

 shall see how beautifully its opening and closing is managed, so that on the stroke the 

 feathers beat the air with their flat sides, but present their sharp edges as they return for 

 another stroke. This movement is copied by the oarsman as he throws back the blade of 

 his oar for another stroke, and is called "feathering" on account of the source from which 

 it is derived. The means by which this object is attained is through a most perfect 

 and beautiful arrangement of the wing muscles, which are so fashioned as to give 

 the wing a slight and involuntary turn just as it is thrown backwards after making 

 its stroke. 



The reader who desires to understand this curious structure, cannot do better than to 

 denude the wing of some bird of its feathers, to remove the skin, and lay bare the muscles. 

 If he then moves the wing as if in flight, he will see, by the play of the different 

 muscles, the part which they take in the general movement, and the wonderful 

 harmony in which every individual muscle works with its fellows. Next let him 

 pass a smooth but blunt edge, such as a small paper-knife, or the flat handle of a scalpel, 

 between the different muscles and separate them throughout their entire length. By 

 pulling each muscle in turn with a pair of forceps, he will see its object, and will be 

 able to form a very good idea of the manner in which all the muscles act while working 

 simultaneously in moving the wing. 



In the generality of birds, the senses of touch and taste seem to be but little developed, 

 while those of sight, hearing, and smell are decidedly acute. 



The sense of touch can be but veiy slight in a creature that is covered with feathers 

 over the whole of its body ; whose limbs are either plume-clad or tipped with horn, and 

 whose mouth is defended by a hard, horny beak. There are exceptions in the case of the 

 ducks, and many similar birds, whose, beaks are soft and evidently possessed of delicate 

 tactile powers, but in the generality of birds this sense is decidedly dull. Taste, again, can 

 have but little development, as the tongues of most birds are devoid of the soft and 

 sensitive surface which is found in the tongue of man and the mammals in general. At 

 the base of the tongue the nerve-bearing papillse are found in some genera of birds, but 

 even in them these organs of taste occupy but a small portion of the tongue, and can give 

 but little indication of savour. In many birds, indeed, such as the woodpecker and the 

 humming-bird, the tongue is employed in a manner analogous to the same organ in the 

 ant-eaters, being used to procure food and to draw it into the mouth. This structure 

 will be described more at length when we come to treat of the birds where it is especially 

 developed. 



The sight of birds is almost invariably remarkable for its development and its adaptation 

 for near or distant objects. The swallow,, for example, when darting through the air with 

 that swiftness which has become proverbial, is capable of accommodating its sight to the 



