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.
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.
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.