The metacarpus consists typically of five members, a number which is never exceeded in any normal terrestrial mammal; the members are numbered from the inner side, beginning with the thumb or _pollex_, from I to V. Many mammals have fewer than five metacarpals, which may number four, three, two or only one; the third is never lost, but any or all of the others may be suppressed, and functionless rudiments of them may long persist as splints or nodules. The metacarpals are elongate, relatively slender and of more or less cylindrical shape; but the form varies considerably in different groups, according to the way in which the hand is used. When employed for grasping, as in many arboreal animals and pre-eminently in Man, the pollex is frequently opposable to the other fingers and enjoys much freedom of motion. In the camels and true ruminants the third and fourth metacarpals are coössified to form a _cannon-bone_ (_see_ Fig. 43, p. 91), but the marrow cavities and the joints for the phalanges remain separate. The phalanges in land mammals never exceed three in each digit, except the pollex, which, when present and fully developed, has but two. The phalanges are usually slender in proportion to their length, but in very heavy hoofed animals they are short and massive. The terminal joint is the _ungual phalanx_, which carries the nail, claw, or hoof, its shape varying accordingly. [Illustration: FIG. 34.—Left femur of Wolf, front side. _h._, head. _gt.tr._, great trochanter. _tr. 2_, second trochanter. _int. con._, internal condyle. _r.g._, rotular groove, _ext. con._, external condyle.] [Illustration: FIG. 35.—Left femur of Horse. _tr. 3_, third trochanter. Other letters as in Fig. 34, than which this drawing is very much more reduced.]