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

Depressions of the radius suited for transmitting and positioning muscles and their tendons.

This is the way the wrist is joined to the radius. In this matter one should further consider that the part of the radius to which its epiphysis is fused, and the epiphysis itself, are depressed and slightly hollow on the inside (n in figs. 1 and 3) not only to make way for the lower of the muscles that pronate the radius (X in the 7th table of muscles) [m. pronator quadratus], but also to provide an exact path for the series of tendons (in the hand in the 5th and 6th table of muscles) which extend from the forearm and serve the flexion of the fingers [m. flexor digitorum superficialis et profundus, flexor pollicis longus]. The outer part of this surface [margo anterior] of the radius 61 is convex because in this way (since it is placed on the outside) it is rendered more stubbornly resistant to injuries. But to prevent the tendons of the muscles 62 from the forearm to the hand that run along this convex surface from slipping off and becoming tangled, several depressions are carved therein through which the tendons covered by transverse ligaments [retinaculum extensorum] (see numbers placed in this spot in the 1st and 2nd table of muscles) are passed as if through rings, as we shall describe in the second book. The depressions of this kind are four in number. The first (g in figs. 2, 4) is wide, provided for the tendons (Z in the 9th table of muscles) which extend the index, middle, and ring fingers [m. extensor digitorum, tendines]. The second (d in figs. 2, 4) transmits the tendon (p in the 10th table of muscles) [m. extensor indicis, tendo] that abducts the index and middle fingers laterally from the thumb. The third (e, z in figs. 2, 4) is more or less a twin


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depression, transmitting the bicornous tendon (L in the 11th table of muscles) of one of the muscles that extend the wrist 63 together with the tendon of the muscle (o in the 10th table of muscles) [m. extensor pollicis longus] that turns or extends the thumb towards the index finger. The fourth depression (h in figs. 2, 4) is very lightly engraved, and scarcely deserves to be called a depression; but there is a rough place that puts forth a ligament [retinaculum extensorum] transversely wrapped around three tendons (k, m, n in the 10th table of muscles and b, c in the 2nd); one of these [abductor pollicis longus] is inserted in the carpal bone that supports the thumb, the second [extensor pollicis brevis] in the first bone of the thumb, and the third [extensor pollicis longus] in the third bone of the thumb. But the surface of the fourth depression is rough and protrudes not just for the sake of that ligament, but also for the stronger insertion of the tendon [m. brachioradialis, tendo] (Q, b in the 12th table of muscles) belonging to the longest muscle that supinates the radius. Besides these depressions, there is another (q in fig. 2) on the outside of the joint where the epiphysis of the radius next to the wrist is articulated to the epiphysis of the ulna, where the tendon of the muscle [m. extensor digiti minimi, tendo] (Q in the 9th table of muscles) is carried which is chiefly responsible for extending the little finger. This depression is believed common to both ulna and radius. 64 Now there is nothing that remains to be said about the ulna and the radius except that they consist everywhere of solid material [os compactum], spongy [os spongiosum] only where the epiphyses are attached to them. They form a hollow space inside [cavitas medullaris] (as appears in the figure inserted in chapter 1) filled with marrow; in this the ulna and radius imitate the humerus, the femur, and the bones of the lower leg.



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