CHARACTERS OF AVES. 



429 



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 attachment of the 

 coracoid bones. 



Fig. 168. A, Breast-bone, shoulder-girdle, and fore-limb of Penguin (after Owen): 

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

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

 Thumb ; tn Metacarpus ; p Phalanges of the fingers. B, Ribs of the Golden Eagle : 

 a a Ribs giving off (b b) uncinate processes ; c c bternal ribs. 



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. 168, 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. 168, 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 



