280 VERTEBRATE ANIMALS. 
usually long and narrow bones. The coracoid bones (£ £) cor- 
respond with the part of the shoulder-blade which is known in 
most of the Mammals as the “coracoid process ;” and in birds 
they are not only separate bones, but they are the strongest 
bones of the pectoral arch. They are more or less nearly verti- 
cal, and they form fixed points for the downward stroke of the 
wing. The collar-bones or clavicles (c) in the great majority 
of birds are united together in front, so as to form a somewhat 
Fig. 151.—A, Breastbone, shoulder-girdle, and fore-limb of Penguin (after Owen) : 
6 Breastbone (stermum), with its prominent ridge or keel; s s Shoulder-blades 
(scapula); & k Coracoid benes; c Furculum or merry-thought, composed of 
the united collar-bones (clavicles); hk Bone of the upper arm or humerus; r 
Radius ; 2 Ulna, forming together the fore-arm ; g Bones of the wrist or carpus; 
¢ Thumb; az Metacarpus ; # Phalanges of the fingers. B Ribs of the Golden 
Eagle; a a Ribs giving off processes (8 4) ; c ¢ Sternal ribs. 
V-shaped bone, which is technically called the ‘“ furculum,” 
but is familiarly called the “merry-thought.” The function 
of this clavicular arch is to keep the wings asunder during 
their downward stroke, and the strength of the furculum varies, 
therefore, with the powers of flight enjoyed by each bird. The 
bones which form the limb proper, or “ wing,” are considerably 
modified to suit the special function of flight, but essentially 
