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Updated: May 6, 2025
I man, II dog, III pig, IV ox, V tapir, VI horse. r radius, u ulna, a scaphoideum, b lunare, a triquetrum, d trapezium, e trapezoid, f capitatum, g hamatum, p pisiforme. 1 thumb, 2 index finger, 3 middle finger, 4 ring finger, 5 little finger. We have not space here to go into the details of Gegenbaur's theory of the skull.
These small digits are so disposed that they could have had but very little functional importance, and they must have been rather of the nature of the dew-claws, such as are to be found in many ruminant animals. The ulna is slightly more distinct than in the horse; and the whole length of it, as a very slender shaft, intimately united with the radius, is completely traceable.
But the most important discovery of all is the Orohippus, which comes from the Eocene formation, and is the oldest member of the equine series, as yet known. Here we find four complete toes on the front-limb, three toes on the hind-limb, a well-developed ulna, a well-developed fibula, and short-crowned grinders of simple pattern.
It is easy to understand the curvature of bones that have passed through a soft stage and also of those that have been broken and badly united, but it is difficult to account for the curvatures that have no such cause; for example, we have seen marked curve of the radius in a forearm of which the ulna was quite straight. The curvature probably resulted from exaggerated growth in length.
But the most important discovery of all is the Orohippus, which comes from the Eocene formation, and which is the oldest member of the equine series, as yet known. Here we find four complete toes on the front-limb, three toes on the hind-limb, a well-developed ulna, a well-developed fibula, and short-crowned grinders of simple pattern.
Examination of the lower end of a young foal's shin-bone, however, shows a distinct portion of osseous matter, which is the lower end of the fibula; so that the apparently single lower end of the shin-bone is really made up of the coalesced ends of the tibia and fibula, just as the apparently single lower end of the fore-arm bone is composed of the coalesced radius and ulna.
Each foot possesses three complete toes; while the lateral toes are much larger in proportion to the middle toe than in Hipparion, and doubtless rested on the ground in ordinary locomotion. The ulna is complete and quite distinct from the radius, though firmly united with the latter. The fibula seems also to have been complete.
Thus, in none of the measurements did the humerus exceed the ulna two inches, which in the Caucasian variety is the lowest number. In all the black races the arm is longer in proportion to the stature than in the white.
The thigh bone corresponds to the humerus; the tibia and fibula to the ulna and radius; the ankle to the wrist; and the metatarsus and the phalanges of the foot, to the metacarpus and the phalanges of the hand. The bones of the lower limbs may be thus arranged: Thigh: Femur, or thigh bone, Lower Leg: Patella, or knee cap, Tibia, or shin bone, Fibula, or splint bone,
But I shall only touch upon those points which are absolutely essential to our inquiry. Let us turn in the first place to the fore-limb. In most quadrupeds, as in ourselves, the fore-arm contains distinct bones called the radius and the ulna. The corresponding region in the horse seems at first to possess but one bone.
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