122 GENERAL ORNITHOLOGY. 
the toes are brought forwards, at right angles or thereabouts with the foot, they spread apart 
from each other automatically in the action, and the diverging toes of the foot thus opened are 
pressed upon the ground or against the water. When the toes are bent around in the opposite 
direction, they automatically come together and lie in a bundle more or less parallel with one 
another, besides being each bent or flexed at their several nodes. The mechanism is best 
marked in the swimmers, which, for advantageous use of their webbed toes, must present a 
broad surface to the water in giving the backward stroke, and bring the foot forward with the 
toes closed, presenting only an edge to the water, —all on the principle of the feathering of oars 
in rowing. It is carried to an extreme in a loon, where, when the foot is closed, the digit 
marked 2¢ in the figure lies below and behind 3¢. It is probably least marked in birds of 
prey, which give the clutch with their talons spread. The jointings of the individual phalanges 
of the toes upon one another are simple hinges, permitting motion of extension to a right line 
or a little beyond in some cases, with very free flexion in the opposite direction. On the 
whole, the mechanics of a bird’s foot are less peculiar than those of the wing, and quite those 
of the limbs of a quadruped. 
In ordinary hopping, walking, and running, and in perching as well, only the toes rest upon 
or grasp the support, from D to beyond, C being more or less vertically over D. Such resting 
of the toes is complete for 2 ¢; 3t, 4¢ in the figure, or for all the anterior toes; but for the hind 
toe it varies according to the length and position of that digit, from complete incumbency, like 
that of the front toes, to mere touching of the tip of that toe, or not even this: the hind toe 
is then sure to be functionless. But many of the lower birds, such as loons and grebes, cannot 
stand at all upright on their toes, resting with the heel touching the ground; and in many such 
cases the tail furnishes additional support, making a tripod with the feet, as in the kangaroo. 
Such birds might be called plantigrade (Lat. planta, the sole; gradus, a step) im strict 
anatomical conformity with the quadrupeds so designated. The others are all digitigrade, 
standing or walking on their toes alone. But no birds progress on the ends of their toes, or 
toe-nails, as hoofed quodrupeds do. A bird’s ordinary walking or running is the same as ours, 
so far as the ordinary mechanics of the motions are concerned ; but its so-called ‘‘ hopping” is 
really leaping, both legs moving at once. Most birds, down to Columba, leap when on the 
ground, a mode of progression characteristic of the higher orders; but many of the more terres- 
trial Passeres and Accipitres progress by ordinary walking when on the ground, as is invariably 
the case with parrots, pigeons, gallinaceous birds, and all waders and swimmers. 
The student need scarcely be reassured that, whatever their modifications, their relative 
development, motions, and postures, the several segments of both fore and hind limbs of any 
vertebrate, quadruped or biped, feathered or featherless, are fixed in one morphologically iden- 
tieal series, thus: 1, shoulder or hip-joint; 2, upper arm or thigh, humerus or femur; 3, 
elbow or knee-joint; 4, fore-arm or leg proper, radius and ulna or tibia and fibula; 5, wrist, 
bend of wing, carpus, or heel, ankle, tarsus; 6, hand proper, metacarpus, or foot proper, 
metatarsus; 7, digits with their phalanges, of hand or foot, fingers or toes. 2, first segment; 
4, second segment; 5, third segment (not separate in foot of bird); 6 and 7, fourth segment, 
in the wing called manus or pinion, in the leg, pes. Observe the improper naming of parts, 
in the case of the hind limb, whereby 1, 2, 3, are not generally counted; 4 is called “thigh”; 
5 is called “‘knee”; 6 is called “leg” or ‘‘ shank”; 7 is called “foot.” Observe also that in 
descriptive ornithology 6 is ‘‘ the tarsus.” 
The Plumage of the Leg and Foot varies within wide limits. In general, the leg is 
feathered to the heel, C, and the rest of the limb is bare of feathers. The thigh is always 
feathered, as part of the body plumage (pteryla femoralis). The crus or leg proper (thigh of 
vulgar language, B to C) is feathered in nearly all the higher birds, and in swimming birds 
without exception ; in the loons, the feathering even extends on the heel-joint. It is among 
