Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 24 On the Bones of the Forearm: the Ulna and Radius

The curvature of the radius

The radius is joined to the ulna above (h in fig. 1) and below (i in fig. 1), while in the middle and through the rest of its length it is so angled in an arc that it separates considerably from the ulna. This is partly the result of a system of movement, to prop the radius with its curved shape on the ulna and to move it readily to supine and prone positions. Another reason was to make it a suitable seat and foundation for the muscles which have to occupy inner and outer places on the forearm. But it is more because of its curving motion than for the sake of the muscles that the radius is curved, and the two bones of the forearm separate farthest in the middle of their course, as we learn from animals whose radius is not pronated and supinated, nor is their hand so moved by the radius. The horse, the sheep, and animals of this kind with solid or cloven hooves, have a radius so attached and bonded to the ulna throughout their length that the radius does not move at all apart from the ulna. In dogs, cats, and those animals whose feet are separated into digits, the radius does move, but as imperceptibly and with as much difficulty as corresponds to the more perfect motion of our hands. In these animals as well, the radius is separated from the ulna, but much less than in man, nor does one see as loose a type of articulation as in man. 46



Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 24 On the Bones of the Forearm: the Ulna and Radius