1, Metacarpal bone.
Tail of moderate length, thick at the base and tapering towards the apex, clothed with short hair_ First hind toe (including the metacarpal bone) absent.
First toe represented by a minute rudiment of a metacarpal bone; the fourth by a metacarpal and two small phalanges without a claw, and not reaching the middle of the metacarpal of the third; fifth entirely absent.
The first metacarpal is short and fuses throughout its length with the second.
Reduction and final loss of outer pair of digits (second and fifth), with coalescence of the metacarpal and metatarsal bones of the two middle digits to form a cannon-bone.
The primitive Artiodactyla thus probably had the typical number (44) of incisor, canine and molar teeth, brachyodont molars, conical odontoid process, four distinct toes on each foot, with metacarpal, metatarsal and all the tarsal bones distinct, and no frontal appendages.
Outer toes small and rudimentary, or in some cases entirely suppressed; their metacarpal or metatarsal bones never complete.
The most interesting genera are, however, the Upper Oligocene and Lower Miocene Gelocus and Prodremotherium, which have perfectly selenodont teeth, and the third and fourth metacarpal and metatarsal bones respectively fused into an imperfect cannon-bone, with the reduction of the lateral metacarpals and metatarsals to mere remnants of their upper and lower extremities.
(3) A line starting above the head of the second metacarpal bone and crossing the hand to the middle of its ulnar border is the line of the head.
(4) The transverse line below this which passes from the ulnar border a little above the level of the head of the fifth metacarpal and ends somewhere about the root of the index finger is the line of the heart.
The folds, therefore, which are disposed for the purpose of making the grasp secure, vary with the relative lengths of the metacarpal bones, with the mutual relations of the sheaths of the tendons, and the edge of the palmar fascia, somewhat also with the insertion of the palmaris brevis muscle.
In the feet the two middle (third and fourth) metacarpal and metatarsal bones, which are completely separate in the pigs, are united at their upper ends.
They give the part of the tongue on which they occur the appearance and feel of a coarse rasp. The feet are furnished with round soft pads or cushions covered with thick, naked skin, one on the under surface of each of the principal toes, and one larger one of trilobed form, behind these, under the lower ends of the metacarpal and metatarsal bones, which are placed nearly vertically in ordinary progression.
In the absence of any trace of the lower extremities of the metacarpal and metatarsal bones of the lateral toes the skeleton differs from the American deer, and resembles those hollow-horned ruminants in which these toes persist.
The lateral metacarpal bones are represented only by their lower extremities; the importance of this feature being noticed in the article Deer.
In the Lower Miocene occurs Protomeryx or Gomphotherium, in which there is a considerable increase in the matter of bodily size, the two metacarpal and metatarsal bones (or those which unite in the latter forms to constitute the cannon-bones) being double the length of the corresponding elements in Protylopus.
This definition will include the living and also most of the extinct forms, although in some of the latter the lateral metacarpal bones not only retain their lower ends, but are complete in their entire length.
- Lateral metacarpal bones represented only by their lower extremities; antlers present in both sexes, complex.
The large metacarpal is called in veterinary anatomy " cannon bone"; the small lateral metacarpals, which gradually taper towards their lower extremities, and lie in close contact with the large one, are called " splint bones."
The carpal joint, corresponding to the wrist of man, is commonly called the " knee " of the horse, the joint between the metacarpal and the first phalanx the " fetlock," that between the first and second phalanges the " pastern," and that between the second and third phalanges the " coffin joint."
2), that of the anterior extensor of the phalanges (corresponding to the extensor communis digitorum of the arm and extensor longus digitorum of the foot of man) passes down over the metacarpal bone and phalanges, to be inserted mainly into the upper edge of the anterior surface of the last phalanx or pedal bone.