AVES. 281 
the same parts are present as in the fore-limb of the Mammals, 
The upper arm is constituted by a single bone, the Aumerus (h), 
which is generally short and stout. The fore-arm is composed of 
two bones, the radius (vr) and the udna (u), of which the ulna is 
the bigger. These are followed by the small bones, which form 
the wrist or carpus (g), but these are reduced to zwo in number. 
The carpus is followed by the bones which constitute the root 
of the hand or metacarpus (m), but these are also reduced to 
two, instead of being five in number, as they are in most Mam- 
mals. The two metacarpal bones are also amalgamated together 
at both ends, so as to form a single piece, at the base of which, 
on its outer side, is a rudimentary digit, the “thumb” (¢), which 
carries a tuft of feathers, known as the “bastard wing.” The 
metacarpal bones, finally, support each a single finger (4), of 
which one is never composed of more than one bone or phalanx, 
whilst the other is composed of two or three phalanges. (To 
understand thoroughly the leading modifications of the limbs of 
birds, the student will do well to refer to the general description 
of the limbs of Vertebrates, pp. 220, 221, figs. 118, 110.) 
As regards the composition of the hind-limb in birds, the two 
halves of the pelvic arch (zz., the zanominate bones) always form 
a single piece each, and they are always firmly united with the 
sacral region of the spine. With the single exception, however, 
of the Ostrich, they do not unite below, but remain separate. 
As in the higher Vertebrates, the lower limb consists of a thigh- 
bone (femur), a shank, composed of two bones (¢/dza and fibula), 
a tarsus, a metatarsus, and phalanges, but some of these parts 
are obscured by coalescence. The thigh-bone or femur (fig. 
152, /), is generally very short, comparatively speaking ; and the 
chief bone of the leg is the ¢dza (2), to which a thin and taper- 
ing fibula (7) is attached. In the regular typical limb of a Ver- 
tebrate animal the tibia and fibula would be followed by a series 
of small bones, called the ¢arsus, constituting the ankle-joint 
(fig. 119) ; and the tarsus would in turn be followed by a series 
of bones constituting the root of the foot, or metatarsus. In 
birds, however, the tibia and fibula are followed by a single 
cylindrical bone, which is called the “tarso-metatarsus” (2), 
and which is formed by the amalgamation of the entire meta- 
tarsus with the whole or a portion of the tarsus. The most 
probable view is that only the /ower portion of the tarsus is 
present in the tarso-metatarsus, and that the wfZer portion of 
