EXTERNAL PARTS OF BIRDS.—THE FEET. 129 
and functional efficiency. In most Passeres it is virtually provided with a special muscle for 
independent movement, so that it may be perfectly apposable to the other toes collectively, 
just as our thumb may be brought against the tip of any finger. In general, it shortens as it 
rises on the metatarsus: and probably in no bird in which it is truly elevated is it as long as 
the shortest anterior toe. It is short, barely touching the ground, in most wading birds; 
shorter still in some swimmers, as the gulls, where it is probably functionless ; it is incom- 
plete in one genus of gulls (Rissa), where it bears no perfect claw: it has only one phalanx 
and is represented only by a short immovable claw in the petrels (Procellartide); it disappears 
in the binds named in the last paragraph but two above, and in some others. It is never actn- 
ally soldered with any other toe. for any noticeable distance ; but it is webbed to the base of the 
inner toe in the loons (Colymbus), and to the whole length of the toe in all the Steganopodes 
(fig. 52). It may also be independently webbed ; that is, be provided with a separate flap or 
lobe of free membrane. This lobation of the hallux is seen in all our sea-ducks and mergansers 
(Fuliguline and Merging). and in all the truly lobe-footed birds, as coots (Fulica), grebes 
(Podicipedide) and phalaropes (Phalaropodide). The modes of union -of the anterior toes 
with one another may be finally considered under the head of the 
Three leading Modifications of the Avian Foot. — Birds’ feet are modelled, ou the 
whole, upon one or another of three plans, furnishing as many types of structure ; which 
types. though they run into one another. and each is variously modified, may readily be appre- 
ciated. These plans are the perching or insessorial, the walking or wading, cursorial or 
grallatorial, and the swimming or natatorial —in fact, so well distinguished are they, that 
earinate birds have even been primarily divided into groups corresponding to these three 
evidences of physiological adaptation of the structure of the Avian pes. Independently of the 
number and position of the digits, the plans are pretty well indicated by the method of union 
of the toes, or their entire lack of union. 1. The insessorial type. (a) In order to make a foot 
the most of @ hand, that is. to fit it best for that grasping function which the perching of 
birds upon trees and bushes requires, it is requisite that the digits should be as free and 
movable as possible, and that the hind one should be perfectly apposable to the others. 
Compare the human hand, for example, with the foot, and observe the perfection secured by 
the perfect fréedom of the fingers and especially the appositeness of the thumb. In the most 
accomplished insessorial foot, the front toes are cleft to the base, or only coherent to a very 
slight extent; the hind toe is completely incumbent, and as long and flexible as the rest. Our 
thrushes (Turdide) probably show as complete cleavage 
as is ever seen, practically as much as that of the 
human fingers; the cleft between the inner and middle 
tue being to the very base. while the outer is only joined 
to the middle for about the length of its own basal 
joint. This is the typical passerine foot (figs. 36, 37. 
42,45). There may be somewhat more cohesion of 
the toes at base, as in the wrens, titmice. creepers, 
vireos, ete.. without, however, obscuring the true pas- 
serine character. As regards this matter, the point is, 
that when the toes are united at all, it is by their actual 
cohesion there, not by movable webbing. Besides the ~ e 
typical passerine. there are several other modifications ie as fg. ts leer 
_of the insessorial foot. (6) Thus a kingfisher shows *éws, nat. size.) 
what is called a syndactyle or syngnesious (Gr. ody. sun. together : ywjows, gnesios, relating to 
way of birth) foot (fig. 44), where the outer and middle toes cohere for most of their extent and 
have a broad sole in common. It is a degradation of the insessorial foot, and not a common 
9 
