Fig. 96.—Third Phalanx of the Horse: Left Anterior Limb, External Surface.
1, Pyramidal eminence; 2, surface, for articulation with the inferior extremity of the second phalanx; 3, basilar process; 4, retrorsal process.
The posterior and inferior borders of these cartilages meet at an acute angle. The angle so formed, or cartilaginous bulb, constitutes the base of the region, which is commonly called the heel—a part of the foot which, as its name implies, is situated posteriorly, but which we must not confound, as we might be led to do, with the region occupied by the calcaneum. We know from our previous studies of comparative osteology that this latter is situated much higher up.
The plantar cushion is a sort of fibrous wedge which occupies the interval bounded by the fibro-cartilaginous plates which we have just been studying. Its inferior surface, the form of which we shall find to be reproduced by a portion of the corresponding surface of the hoof, is prolonged anteriorly into a point, while behind it is divided into two branches, which, diverging from one another, join the posterior angles of the fibro-cartilages. These two branches are separated by a median excavation.
The different constituent elements which we have just been discussing give elasticity to the foot.
To finish the examination of the parts contained in the hoof, we will add that among them is also found what is called the fleshy envelope, or flesh of the foot.
We divide the latter into three regions: the podophyllous tissue, striated or laminated flesh which is spread out over the anterior surface of the third phalanx; the pad, or the hardened skin which corresponds to the upper border of the hoof, and forms a prominence above the podophyllous tissue; and the villous flesh, or velvety tissue which covers the plantar surface of the third phalanx and the plantar cushion. These three tissues form as a whole the keratogenic membrane—that is to say, that which produces horny tissue, and consequently regenerates the hoof.
It is this latter that we now proceed to study.
