BIRD. 



diate between the two, and partaking of the properties 

 of both. The average line, or axis, of its motion is 

 oblique, elevated to the front, and depressed to the 

 rear, but both the principal head of the humerus and 

 the socket have their outlines curved, so that the 

 wing may be advanced or drawn backward at the 

 same time that it is elevated or depressed, and by 

 some of the muscles acting more and some less, all 

 the motions of the shoulder-joint, which are requisite 

 both for the action of flight and the direction of that 

 action, are performed. The double head of the 

 humerus, which may be understood by looking back 

 to the wing of the jer-falcon, or forward to the sternal 

 portion of the skeleton of the golden eagle, assists 

 very materially in both the direct and the oblique 

 motions of this joint. In proportion as the action of 

 the wing is more powerful, the crest of the humerus, 

 that is, the process or portion of the head which is 

 toward the convex side of the bone, or that which is 

 most in advance when the bone is in its natural 

 position, is more produced. It is more so in the 

 humerus of the jer-falcon than perhaps in that of any 

 other bird, and more so in the falcons which prey on 

 the wing than in any other genus of birds. 



The second set of muscles in the wing are those 

 which are inserted on the coracoid, and attached to 

 the humerus and the radius. There are two of them 

 attached by a common tendon to the external part of 

 the extremity of the coracoid, near the glenoid cavity, 

 but below it. The coraco-branchial is attached to 

 the crest of the humerus, and acts as the antagonist 

 of the third pectoral, and extends the humerus from 

 the body. The biceps is attached to the radius, and 

 extends the fore-arm or great medial portion of the 

 wing. 



There is only one single muscle inserted in both 

 the shoulder-bone and the coracoid. It has its 

 insertion in the lower side of the shoulder bone and 

 the upper edge of the coracoid, and its tendon is 

 inserted in the head of the humerus, on the lower 

 side, by the edge of the insertion of the smaller 

 pectoral muscle. Its office is to close the wing 

 toward the body, but it of course acts only on the 

 humeral portion. 



The next set of muscles are those which are 

 attached to the scapula or shoulder-bone only, and 

 act between that bone and either the humeral or the 

 radial portion of the wing. Th?y are three in number. 

 The first is attached to a greater or smaller portion 

 of the external edge of the scapular bone, sometimes 

 in two separate fasciculi of fibres, and sometimes with 

 the two fasciculi united by a tendinous septum. 

 When the latter is the case, it is inserted by one 

 tendon in the posterior edge of the humerus, below 

 the cavity ; and in the former, by a tendon and a 

 fasciculus of muscular fibres to nearly the same point. 

 The use of this muscle is to draw the humerus toward 

 the body of the bird, and at the same time to raise it 

 upwards. The second of these muscles is inserted 

 by a very strong tendon to the glenoid cavity, and it 

 is attached to the humerus. Its office is to draw the 

 wing toward the body, and raise it, and also to extend 

 the fore-arm, or radial joint of the wing. The third 

 of these muscles is a long and slender fasciculus, 

 which, originating in the lower and exterior part ol 

 the scapular bone, behind the last-mentioned one, 

 is attached to the scapula, and appears chiefly an 

 auxiliary to the former. 



There are tw r o muscles originating in the scapula, 

 the clavicle and the coracoid, which chiefly assist in 

 elevating the wing, or in advancing it, or bending it to 

 the rear, when the bird is in flight. But the actions of 

 these secondary muscles, which are efficient chiefly 

 in altering the direction of the birds in flight, upward, 

 downward, or laterally, cannot be fully explained 

 without more space, and more illustrative figures, 

 than are compatible with the nature, and indeed the 

 purpose, of this brief sketch. The whole of the mus- 

 cular actions of a wing form a very extensive as well 

 as a very nice subject for study, and one which can 

 be very imperfectly comprehended even by those 

 who devote their whole time and their best attention 

 to it. The reason is obvious : the actions of the 

 numerous muscles of the wing are so combined with 

 each other, and the action of the one modifies that of 

 the other so much, that the most minute definition, 

 and the most careful study, are incapable of informing 

 us how the wing acts in all its varied motions ; so that 

 the utmost which, in the present state of science, we 

 can expect to obtain, is a very rude and imperfect 

 estimate of the relative powers of wings, derived fully 

 as much from what we see them performing in the 

 living bird, as from any thing apparently more scien- 

 tific (and it is mere appearance rather than reality) 

 which we find in dissecting the dead one. 



In giving a few examples of the form of the sternum, 

 and its apparatus, the coracoids, the clavicle, and the 

 scapulars, as illustrative of the power of flight in birds, 

 we shall not attempt to follow even the outline of a 

 system proposed by M. Lherminier, because that is 

 incomplete, as treating of the sternal apparatus with 

 reference to flight only, and not combining the general 

 character of the class, the support which the body 

 receives from the sternal bones, altogether inde- 

 pendent of power of flight ; and also because, though 

 very ingenious and scientific so far as it goes, the 

 sketch which he gives is not perfectly satisfactory, 

 even in so far as the mere action of flying is con- 

 cerned. The sternum and the sternal apparatus, 

 whether of bones or of muscles, are not the whole 

 organs of flight, we have still to take into account 

 the bones and muscles of the wing, and the character 

 of the feathers with which that wing is furnished ; 

 and even if we were put fully in possession of these, 

 there still remains the accordance of the other struc- 

 tures of the bird with the entire wing, as relates to 

 the style of flight, and also to those other actions of 

 the bird with which the flight is always in accordance. 

 In consequence of these difficulties, which volumes 

 of writing would not explain away, we must content 

 ourselves with a few short notices of the sternal 

 apparatus of the leading division of birds, as formed 

 on the usual mixed characters. 



Sterna of the Accipitrcs. This is firm, though the 

 thicker parts of it are full of air-cells, more especially 

 the enlarged base of the keel, which passes, by a 

 gradual curvature, into the surface of the sides of the 

 sternum, without any corresponding cavity on the 

 upper side, or side toward the interior of the bird. 

 Its form is nearly that of a parallelogram, with the 

 length exceeding the breadth, concave on the upper 

 side, and convex on the under. The keel generally 

 large and elevated, but always lower the broader 

 the sternum is in proportion to its length. The 

 anterior margin of the keel is concave, and the 

 under one convex ; the anterior anerle sometimes 



