During flexion, the anterior surface of the foot tends to approach the anterior surface of the leg, the angle formed by these two segments becoming more and more narrowed. The displacement in the opposite direction characterizes extension. In other quadrupeds, the articulations which bind together the bones of the tarsus possess a little more freedom of movement. The shape of these bones, and particularly the shape of the surfaces of the astragalus, which are in contact with them, allow movements in this region, in the case of the dog and cat, which, without being so extensive as those of the human foot, in the subastragaloid articulation, nevertheless, recall the mobility which we find in the human species at this level--that is to say, rotation, abduction, and adduction of the foot. As for the articulations of the metatarsus with the phalanges, and of the phalanges with one another, they resemble those of the anterior limb too closely that it should be necessary to study them here. Such a study would be, in this case, but a repetition (see p. 76, a description of the articulations in question). THE HEAD IN GENERAL, AND IN SOME ANIMALS IN PARTICULAR When we compare, by the examination of one of their lateral aspects, the skull of man and the same region in other mammals, it is easy to observe that the relative development of the cranium and face is entirely different. In the case of man the cranium is large, and the face relatively small; in animals the face is proportionally much more highly developed. The measure of the facial angle permits us to note these differences, and the figures relative to the value of this angle are sufficiently demonstrative to induce us to indicate those which are, in a general way, connected with some of the forms in individuals which here occupy our attention. In the first place, we must remember that the angle in question is more acute, as the cranium is less developed in proportion to the facial region (Figs. 56 and 57). It is especially to this character that we wish to draw attention. Man 70°-80° Cat 41° Dog 28°-41° Sheep 20°-25° Ox 18°-20° Ass 12°-16° Horse 11°-13° Besides, in animals the cranium is very prominent superiorly, and the face, more or less elongated, is sharply projected downwards and forwards; in man the cranial region occupies not only the superior, but also the posterior part; the face is short and of a compact form. The human head, in its general aspect, may be compared to a sphere, while the skull of the quadrupeds presents the aspect of a quadrangular pyramid, with the base turned upwards and the summit at the incisor teeth. =Direction of the Head.=--Before entering on the study of the bones of the head, it is necessary, in our opinion, to agree as to the position in which we shall suppose it to be placed.