VERTEBRATA: AVES. 



579 



portion of the glenoid cavity for the articulation with the nead 

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

 formed by the coracoid. The coracoid bones (fig. 323, A, k k) 

 correspond with the coracoid processes of man ; but in birds 



Fig. 323. A, Breast-bone, shoulder-girdle, and fore-limb of Penguin (after Owen) : 

 b Sternum, with the sternal keel ; j s Scapulae ; k k Coracoid bones ; c Furculum or 

 merry- thought, composed of the united clavicles; h Humerus : u Ulna; r Radius; 

 / Thumb ; m Metacarpus ; p p Phalanges of the ringers. B, Ribs of the Golden 

 Eagle : a a Ribs giving off (b b) uncinate processes ; c c Sternal ribs. 



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 

 glenoid 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. 323, 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" (" four- 

 chette" of the French). The outer extremities of the furculum 

 articulate with the scapula and coracoid ; and the anchylosed 



