Although the wall forms a continuous whole, it has been divided into regions to which special names are given. The anterior part, from the superior border to the inferior, is called the _pince_ or _toe_ for a width of 4 to 5 centimetres. External to the toe, and on each side of it, for a distance of 3 or 4 centimetres, is the _nipple_. Behind the _nipples_ are the _quarters_. Still further back, where the wall folds on itself, forming the _buttress_, is found the region of the _heels_. Finally, the portions of the wall which form its continuation in passing forward are called the _bars_.[36] These are only visible on the inferior surface of the hoof (see Fig. 100). [36] It is to the angle of inflexion or heel that some authors give the name of buttress; it is the bars which other authors designate in this fashion. The wall, convex transversely, is, in its anterior part (viz., the _toe_) inclined strongly downwards and forwards. This obliquity tends to become gradually effaced on the lateral parts to such a degree that at the quarters it becomes almost perpendicular to the surface of the ground. The internal quarter is less rounded than the external; in addition to this (Fig. 97), it approaches more nearly to the vertical direction. [Illustration: FIG. 98.--LEFT ANTERIOR FOOT OF THE HORSE: EXTERNAL ASPECT. 1, Fetlock; 2, spur or beard; 3, pastern; 4, outline determined by the external fibro-cartilage; 5, acute angle; 6, nipple; 7, quarter; 8, heel.] In our opinion, this latter difference clearly recalls certain characters of the general form of the human foot. In fact, the latter has its dorsal surface inclined downwards and outwards, whereas its internal border may be said rather to be vertical. A transverse section of the foot (Fig. 99) justifies this comparison, which to us appears interesting, not only as regards the resemblance which exists between these organs of support, but, further, because it constitutes a mnemonic which enables us, on condition that we remember the form of the human foot, to recall the above-described character of that of the horse. The greater convexity of the outer portion of the hoof is found equally on the human foot; the external border of this foot is more convex than the opposite one. The inferior border of the wall (Fig. 100) is, in the case of unshod horses, always in wear when in contact with the ground. It is intimately united to the circumference of the sole (see further on). [Illustration: FIG. 99.--VERTICAL AND TRANSVERSE SECTION OF A LEFT HUMAN FOOT: OUTLINE OF THE DIVIDED SURFACE OF THE POSTERIOR SEGMENT OF THIS SECTION (DIAGRAMMATIC FIGURE). AA´, Vertical axis passing through the middle of the leg and the second toe; 1, outer side; 2, inner side.] The superior border is hollowed on its internal surface by a groove, the cutigerous cavity or basil, which lodges the cushion (see Fig. 95). We have described this latter above, in connection with the flesh of the foot.