Fig. 94.—Left Hand of the Dog: Inferior Surface, Plantar Tubercles.
1, 1, 1, 1, 1, Tubercles of the fingers; 2, plantar tubercle; 3, tubercle of the carpus.
Plantar Tubercles ([Fig. 94]).—These tubercles, or dermic cushions, are divided, in each paw, into tubercles of the digits (or of the toes), a plantar tubercle, and, on the fore-limbs, a tubercle of the carpus.
The tubercles of the fingers (or of the toes) are of the same number as the latter. That which belongs to the thumb is but little developed, but the others are more so. They are in relation with the plantar surfaces of the second and third phalanges, so that when the paw is in contact with the ground the articulation which, in each of the fingers or toes, joins these phalanges, rests on the corresponding pad.
The plantar tubercle is larger than the preceding. It is of a more or less rounded form; sometimes it is triangular, and then comparable in outline to the ace of hearts, the point of which is, in this case, turned towards the claws; its margin being sometimes strongly indented, it may also have a trilobate form. It is on it that rest the metacarpo-phalangeal or metatarso-phalangeal articulations, according to the limb studied. The tubercle of the carpus, situated at the level of the posterior surface of this latter, is less important than the preceding, the region which it occupies not reaching the ground during walking. But it is not to be neglected from the point of view of external form, because of the prominence which it produces.
In the ungulates the terminal extremity of the limb is, as we have above pointed out, enclosed in a horny envelope which is no other than the hoof.
We will first study the hoof of the horse—a hoof which is single for each of the limbs, inasmuch as in this animal each of these has but a single digit.
Hoofs of the Solipeds.—We will first study the hoof as regarded in a general way—that is, without taking into account the limb to which it belongs. We will afterwards point out the differences presented when the hoofs of the fore and hind limbs are compared.
In connection with the external forms of the horse, the study which we are now commencing is of great importance. But, before entering upon it, it appears to us necessary to rapidly examine what the hoof contains ([Fig. 95]).