AVES. 



281 



muscles (pectoral muscles) which move the Aviiigs. As a general 

 rule, the size of this crest or keel gives a tolerably just estimate 

 of the tiyiug powers of the bird to which it belongeil. The keel is, 

 of course, mcjst largely developed in those birds which possess the 

 power of flight in its greatest perfection ; and in certain birds which 

 do not fl)', such as the Ostrich, there is no sternal keel at all. The 

 pectoral arch or shoulder-girdle of birds, consists of tlie shouldei'- 

 blades {scapula;), the clavicles or collar-bones, and of two bones, 



Fig. 2J2. — A, I3re^st-buiie, s]iuul<ier-gii-d;c, ami fure-liliil* of Penyuiii (alter Owen); b 

 Breast-boiie (sternuDi), ^vith its itrniuiiieiit ridge or keel; a' s Slioulder- Ijlbdes 

 (scaimloi) , h k Coracnid bones; c Furculuni or nicn-y-tliouglit, composed of tlie 

 united collar-bones {doAncUii)\ h Bene of the ujiiier arm or innncrvf:, r Radius, 

 and u Ulna, forming together the fore -arm ; (] Bones of the wrist or carpvjs ; t 

 Thumb ; m Metacarpus ; p Phalanges of the finficrs. B, Ribs of the G(dden Eagle : 

 a a Ribs giving off processes {h h); c c Sternal RiVis. 



which are distinct in Birds, and ai'e called the " coracoid bones.' 

 The shoulder-blades (.s s) are usually long and narrow bones. The 

 coracoid bones U- k) correspond with the jiart of -the shoulder-blade 

 which is known in most of the Mammals as the " coracoid pro- 

 cess " ; and in Birds they are not only separate bones, but they are 

 the strongest bones of the pectoral arch. They arc more or less 

 nearly vertical, and they form fixed points for the downward stroke 

 of the wing. The collar-bones or clavicles (<■) in the great majority 

 of Birds are united together in front, so as to form a i:;omewhat V- 



