The toes are, in the majority of species, four in number:[15] an internal, which is directed backwards, and corresponds to the great-toe; the others are directed forwards. This arrangement is constant in grallatores (wading birds), gallinaceæ[16] (domestic fowls), and raptores (birds of prey). [15] In spite of the fact that the custom is to designate the terminal portions of the foot of birds by the name of digits, we prefer to employ here the terms _foot_ and _toes_. In adopting this decision we believe we are acting according to a more didactic method. Homology of names should, in our opinion, always accompany homology of regions. [16] With regard to the gallinaceæ, we must add that in certain varieties the number of toes is five; those which are directed forwards are three in number; the internal one which passes backward, is double. The two toes which are the subject of this special arrangement are placed very close together, and are nearly always superimposed. This condition is found in the Houdan and Dorking breeds. [Illustration: FIG. 47.--POSTERIOR LIMB OF THE HORSE PLACED IN THE POSITION WHICH IT SHOULD OCCUPY IF THE ANIMAL WERE A PLANTIGRADE: LEFT LIMB, EXTERNAL SURFACE. 1, Tibia; 2, astragalus; 3, calcaneum; 4, metatarsus; 5, first phalanx; 6, second phalanx; 7, third phalanx.] In climbing birds (parrots, woodpeckers, and toucans), the innermost toe is not only directed backward, but the external toe accompanies it in that direction; consequently, there are two posterior and two anterior toes. Sometimes they are all directed forwards; this disposition is found in the martins. In some birds, the number of toes is reduced to three: the cassowary shows this reduction; in others, the number is still further diminished--the ostrich, for example, has but two. [Illustration: FIG. 48.--SKELETON OF THE FOOT OF A BIRD (THE COCK): LEFT SIDE, EXTERNAL SURFACE. 1, Metatarsus; 2, spur; 3, rudimentary metatarsal; 4, first toe; 5, second toe; 6, third toe; 7, fourth toe.] Further, we find that, in general, the number of the phalanges increases, when we examine the toes in commencing with the most internal (Fig. 48): this has two; then the following one three; that which comes next in order has four; and the most external toe has five. The phalanges of this last are short; so that, although it is formed by a larger number of bones, it is not the longest of the toes. THE POSTERIOR LIMBS IN SOME ANIMALS. =Plantigrades=: =Bear= (Fig. 33, p. 50).--The external iliac fossa is very deep. The femur is longer than the bones of the leg; the great trochanter does not reach the level of the head of the femur. The fibula is well developed; it is united to the tibia at its superior and inferior extremities only.