44 PLUMAGE OF THE LEG. 
prongs have such mutual obliquity, that when the toes are brought forward, 
at right angles or thereabouts with the tarsus, they spread themselves in 
the action, and the open foot, with its diverging toes, are pressed on the 
ground or against the water; and when the toes are bent around in the other 
direction, they close together more or less parallel with each other, besides 
being bent or flexed, each one at its several nodes. The mechanism is best 
illustrated in the swimmers, which must present a broad surface to the water 
in giving the backward stroke, and bring the foot forward closed. with only 
an edge opposed to the water. It is carried to such extreme in the loon, 
that the digit marked 2¢ in the figure lies below and behind 3¢, as there 
shown; in most birds with the foot in much the same position relative to the 
tarsus, 24 would appear above 3¢ (compare other figures of feet). It is 
probably least marked in birds of prey, that clutch with all the toes spread. 
The individual toe joints are all simple hinges. 
(b.) In ordinary hopping, walking, perching, etc., only the toes rest upon 
or grasp the support, and c is more or less perpendicularly above p. This 
resting of the toes is complete for all the anterior ones; for the hind toe it 
varies according to the position and length of the latter from complete 
resting like the others, to mere touching of the tip, and finally to not 
even this; the hind toe is then said to be functionless. But the lowest 
birds cannot stand upright on their toes at all; these rest with the tarsus 
horizontal, and the heel c touching the ground; moreover, in all these birds, 
the tail affords additional support, making a tripod with the legs, as in the 
kangaroo. These birds might be called plantigrade, in strict anatomical 
analogy with the beasts so called; the others are digitigrade, quite as analo- 
gously ; but there are no birds, that, like horses and cows, walk on the ends 
of their toes, or toe-nails. A bird’s ordinary walking or running, corres- 
ponds exactly with ours, as far as the mechanics of motion are concerned ; 
but its hopping, as it is called, is really leaping, both legs being brought 
forward at once. Nearly all birds down to Gallince, leap when on the 
ground; all others walk or run, advancing one leg after the other. Leaping 
is thus really distinctive of the ZJnsessores; though many of them, as tit- 
larks, shore larks, meadow larks, many terrestrial sparrows, blackbirds, 
crows, turkey buzzards, and others, including all the pigeon family, walk 
instead of leaping. 
§ 74. Tue Prumace of the legs varies within wide limits. In general, 
the leg is feathered to the heel, and the tarsus and toes are naked. The 
thigh is aways feathered. The crus is feathered in all Jnsessores (with 
rare exceptions), and in all Watatores without exception; in the loon family 
the feathering extends on as well as to the heel-joint. It is among the Cur- 
sores, or walkers, and especially wading birds, that the crus is most naked ; 
here it may be denuded half way up. A few waders—among ours, chiefly 
in the snipe family —have the crus apparently clothed to the joint, but this 
is in most if not all cases due to the length of the feathers, for probably no 
one of them has the crural pteryla itself extended to the joint. The crural 
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