STRUCTURE OF THE WING OF A BIRD. 



237 



BOXES OF WING OF BIRD. 



(After Sundevall.) 

 (a) Humerus: (B) Cubitus ; (<:) Ulna; 

 (d) Radius ; (E) Manus, or hand ; 

 (/) Carpus; (g, ft, i) Metacarpus: 

 (*) Pollex, or thumb; (I) Second 

 digit ; (HJ) Third digit. 



that of the Mammalia by from 8 to 14, is maintained by its admirable feather-clothing, which, being 

 a non-conductor, effectually serves to guard against any sudden variations of temperature in the air 

 to which its body is exposed, during its rapid and extensive flights, as well as tempering the usual 

 radiation from the body. 



As one might expect in the fore-limb of a creature specially organised for suspension in, and pro- 

 gression through, the air, it is found that the muscles, as well as the bones and joints, of the bird's 

 wing become much modified as compared with the corresponding parts of 

 other animals. With all our scientific knowledge and mechanical contri- 

 vances, no one has yet succeeded in constructing a flying machine. It 

 is a significant fact that Nature has not only long ago solved this problem, 

 but that she has done so in several ways. The flight of an insect, of a 

 bird, of a bat, is equally perfect in its way : but in each case the result 

 is attained by very different modifications in the skeletal and muscular 

 apparatus. The principal resistance that a flying animal has to work 

 against is its weight : that is, the force of gravity which, proportionately 

 to its mass, tends to draw it down vertically towai-ds the earth hence the 

 muscles which are largest and strongest in a bird are those which pull 

 down the wing against the air, thereby raising the body and overcoming its 

 weight. 



The chief muscle thus employed is the " great pectoral," attached to 

 the large keel (or ridge) on the breast-bone, and inserted into the " hurnerus," or " arm-bone." This 

 " great pectoral " is generally the largest muscle in the bird's body, and in fact often equals in bulk 

 all the other muscles put together. 



The wing is opened out by straightening the elbow and the wrist-joints. The former process 

 is effected by the contraction of the triceps ; the latter chiefly by the action of the so-called " radial 

 extensors," and by the elasticity of the long " tensor," or ligament, which comes from the shoulder 



muscles along the front border of the anterior 

 wing-membrane, and is attached to the base of the 

 thumb, at the front side of the wrist. 



The wing is folded by the bending of the elbow 

 and the adduction of the wrist-joints. The elbow 

 is bent principally by the contraction of the "biceps" 

 and the "internal brachial," the wrist-joint chiefly 

 by the contraction of the "hand-adductor," and of 

 the " ulnar wrist-flexor." 



As already stated, the possession of feathers is 

 one of the most characteristic features in a bird. 

 These beautiful structures are modifications of the 

 skin, just as are the scales of the feet and the claws 

 of the toes. Feathers and hairs, scales and claws, 

 are all produced out of, and are modifications of, the cells of the upper skin, or epidermis, and of the 

 under, or true skin, or cutis. The feathers differ much in their minute construction in some birds ; 

 and all those of a bird are of course not of the same size and shape, but they have the following 

 parts in common. 



A feather consists of a quill, a shaft, barbs, and barbules : moreover, there may be a kind of 

 accessory part, often in the shape of a downy tuft, close to the junction of the shaft and the quill- 

 The shaft (scapus) or axis of every perfect feather (penna) is divided into the quill (calamus), the 

 hollow cylinder (d), which is partly embedded in a sac of the skin, and the true shaft (rachis, a), 

 which bears on each side the lateral processes called barbs (rami or radii). The rachis and the barbs 

 together are known as the vane (vexilhtm), and, in fact, form what is commonly known as the 

 "feather" in contradistinction to the "quill." The barbs (c, c, c, c) are narrow plates, or laminae, 

 " tapering to points at their free ends, and attached by their bases on each side of the rachis. The edges 

 of these barbs are directed upwards and downwards, when the vexillum of the feather is horizontal 

 125 



FEATHERS OF WING OF BIRD. (After Sv.ndeva.ll.) 



(Al Feathers of the manus, or primary quills: (B) Feathers of the 

 cu'>i'n->, or secondary quills; (c| Coverts of the matins, or primary- 

 coverts; (D) Lesser primary-coverts; (E) Coverts of the cvititus, or 

 secondary-coverts; (p) Median coverts; (o) Lesser coverts; (H) 

 Feathers of the thumb, or bastard wing. 



