BONES OF THE SHOULDER. 367 



any ridge on its front surface ; but in other Birds there is a kind 

 of projecting and longitudinal keel, (, Fig. 180), which gives 

 more power to the muscles which draw down the wing. 



329. The shoulder bones also are so disposed as to give the 

 greatest power to the wings. The scapula (0, Fig. 180), is narrow, 

 but much lengthened in the direction parallel to the spine ; and 

 is supported on the sternum not only by the clavicle (/), but also 

 by another bone (c) which fills the office of a second clavicle, 

 and which is called the cgracoid bone, from its apparent analogy 



to the coracoid process of the 

 human scapula. The cla- 

 vicles of the two sides are 

 generally united at their an- 

 terior extremity in the form 

 of a V, whose point is directed 

 downwards, and are attached 

 to the keel of the sternum ; 

 this compound bone is termed 

 the furcula^ and in common 

 language the merry-thought. 



FIG. 180 BONKS OF THE SHOULDER AND The COracoid bones Constitute 



the buttresses, which, with 



the furcula, keep the shoulders separated, and afford to the 

 humerus a point of support, so much the firmer as the Bird is a 

 better flyer. In Birds which fly but little, or not at all, the 

 clavicles have, on the contrary, but a slight development. Thus 

 in certain terrestrial Parroquets of Australia, these bones are 

 completely rudimentary ; in the Cassowary and American 

 Ostrich they are represented only by slender-pointed processes ; 

 in the African Ostrich and the Toucans, they almost reach the 

 sternum, but are not united together at their lower extremities ; 

 among some Owls they are united by a cartilage; whilst in 

 most Birds their union is complete, and they are often directly 

 supported on the sternum, by means of a central projection from 

 the point of union. 



330. The anterior members of Birds never serve either for 

 walking, prehension, or touch ; but form lateral expansions 



