CHARACTERS OF BIRDS. 385 



attached the great pectoral muscles, which move the wings. 

 As a general rule, the size of this sternal crest allows a very 

 tolerable estimate to be formed of the flying powers of the 

 bird to which it may have belonged ; and in the Ostriches and 

 other birds which do not fly, there is no sternal keel. At its 

 anterior angles the sternum exhibits two pits for the attach- 

 ment of the coracoid bones. 



The scapular or pectoral arch consists of the shoulder-blade 

 or scapula, the collar-bone or clavicle, and the coracoid bone, 

 on each side. The scapula, as a rule (fig. 329, A, s s) is a 

 simple elongated bone, not flattened out into a broad plate, 

 and carrying no transverse ridge, or spinous process. Only a 

 portion of the glenoid cavity for the articulation with the head 

 of the humerus is formed by the scapula, the remainder being 

 formed by the coracoid. The coracoid bones (fig. 329, A, k k) 

 correspond with the coracoid processes of man, but in birds 

 they are distinct bones, and are not anchylosed with the scap- 

 ula. The coracoid bone on each side is always the strongest 

 of the bones forming the scapular arch. Superiorly it articu- 

 lates with the clavicle and scapula, and forms part of the gle- 

 noid cavity for the humerus. Inferiorly each coracoid bone 

 articulates with the upper angle of the sternum. The position 

 of the coracoids is more or less nearly vertical, so that they 

 form fixed points for the action of the wings in their down- 

 ward stroke. The clavicles (fig. 329, A, c) are rarely rudimen- 

 tary or absent, and are in some few cases separate bones. In 

 the great majority, however, of birds, the clavicles are anchy- 

 losed together at their anterior extremities, so as to form a 

 single bone, somewhat V-shaped, popularly known as the 

 " merry-thought," and technically called the " furculum." The 

 outer extremities of the furculum articulate with the scapula 

 and coracoid ; and the anchylosed angle is commonly united 

 by ligament to the top of the sternum. The function of the 

 clavicular or furcular arch is "to oppose the forces which tend 

 to press the humeri inwards towards the mesial plane, during 

 the downward stroke of the wing " (Owen). Consequently the 

 clavicles are stronger, and their angle of union is more open, 

 in proportion to the powers of flight possessed by each bird. 



As regards the structure of the wing proper, the humerus is 

 short and strong, and articulates superiorly with an articular 

 cavity formed partly by the coracoid and partly by the scapula. 

 The fore-arm is composed of a radius and ulna, of which the 

 former is the smallest and most slender. The carpus is reduced 

 to two small bones wedged in between the distal end of the 

 fore-arm and the metacarpus. The metacarpus consists of 



2 B 



