CHARACTERS OF AVES. 



459 



powers of flight extends over the abdominal cavity as well, in 

 some cases even reaching the pelvis. The sternum of all 

 birds which fly, is characterised by. the presence of a greatly- 

 developed, median ridge or keel (fig. i8o, A), to which are at- 

 tached the great pectoral muscles which move the wings. As a 

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

 estimate tp be formed of the flying powers of the bird to which 

 it may ha^e 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. , , 



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. i8o, A, s s), is a 



Fig. 180. — A, Breast-bone, shoulder-girdle, and fore-limb of Tenguin {after Owen): 

 J Sternum, with the sternal keel ; s s Scapulae : A & Coracoid bones ; c Furculum or 

 merry-thought, composed of the ut^ited clavicles ; Jt Humerus ; u Ulna : r Radius ; i 

 Thumb ; m Metacarpus ; ^ Phalanges of the finders. B, Ribs of the Golden Eagle : 

 a a 'Ribs giving off (&^. uncinate processes; c c bternal ribs. 



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

 and carrying no transverse ridge, or-^pinous 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. 180, A, /i k) 

 correspond with the coracoid processes of man ; but in birds 

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