146 BIRD GALLERY. 



as the unciaate processes (fig. 5 ii & fig. 7i). These are flat blade- 

 shaped bones attached to the middle of one rib and sliding over the 

 outer surface of that immediately behind it. 



The breast-bone or sternum (fig. o 12) is a large, broad, more or less 

 convex bone which protects not only the thorax, but also a part of the 

 abdomen. In all birds in which the fore-limbs act as the principal 

 organs of locomotion, this breast-bone is provided with a deep crest 

 or keel (1.3) for the attachment of the muscles of flight. In proportion 

 as the power of flight is diminished, this crest becomes less prominent 

 and may disappear altogether. 



The pectoral arch or shoulder-girdle consists of three pairs of bones — 

 the pillar-like coracoids (fig. 5 14), the scapulae or shoulder-blades (15), 

 which are narrow and sabre-shaped, and the clavicles or collar-bones 

 (le), which are generally united at their lower end and form a 

 V-shaped bone, the furcula, commonly known as the *' merry-thought." 

 The principal support of the attachment of the wing to the trunk is the 

 coracoid, which is broadly joined to the anterior extremity of the 

 sternum and forms, together with the scapula, the base of attachment 

 for the humerus or upper arm-bone. The fore-limb consists of the 

 following parts: — the upper arm-bone {humerus) (17), forearm [ulna 

 Sind radius) (is, 19), two small free wrist-bones (20^ 21) (carpals), an 

 elongate hand {carpo -metacarpus) (22), and three fingers {dibits). Of 

 the latter, the thumb [pollex) (23) is a sitigle styliform bone joined to the 

 first metacarpal and bearing the so-called "bastard-wing" (fig. 2 8); 

 the second or index-finger (24) is tlie longest, composed of two or 

 three joints, and forms the extremity of the wing, while of the third 

 (2.')) there is only a vestige. The thumb and index digit are sometimes 

 furnished with a claw. 



Thej9e/m*«of Birds is open in front, a union or symphysis of the 

 pubic bones (26) occurring only in the Ostriches. The shape of the 

 pelvis is remarkable from the great forward prolongation of the iliac 

 bones (27), which may extend forwards on to the ribs. The acetabulum 

 or socket for the articulation of the hind limb occupies a position about 

 half way between the extremities of the pelvis; the centre of the cavity 

 is unossified and appears as a round perforation. 



The hind limb consists of the following parts : — the thigh-bone 

 [femur) (29) ; lower leg (composed of the united tibia audjibula (30, .3 1 ), to 

 which are fused the proximal elements of the ankle or tarsvs) ; the foot 

 [tarso-metatarsus (32), composed of the distal elements of the tarsus 

 fused with the metatarsus and forming a long bone, generally though 

 incorrectly called the leg) ; and normally four toes [dibits). The most 

 characteristic bone of the leg is the tarso-metatarsus, which terminates 

 in thres articular heads for the attachment of the three front toes in the 



