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

What the ulna has along its length

First of all, the lower end 43 of the ulna is somewhat convex (X, Y, Z in fig. 6, V in the 9th table of muscles) at the root of its posterior process next to the humerus, where we lean on our elbow, resembling a triangle in its breadth. It is unfleshed and not covered by muscles, and it is seen as soon as the skin is removed, receiving only the sinewy fascia of muscles (S, T in the 9th table of muscles) 44 by which the forearm is extended. The apex of this triangle (from Z through a, a in figs. 2, 6; a, a in figs. 1, 2) runs down along the ulna, and protrudes in a line [margo posterior] chiefly because the sides of this line are compressed by two muscles and the ulna itself yields to these muscles, one of which (L in the 9th table of muscles) [m. extensor carpi ulnaris] runs along the outer side of the line, being inserted in the metacarpal bone before the little finger and extending the wrist. The other [m. flexor carpi ulnaris] (C in the same table), which runs along the inner side and to which the ulna gives way more, is inserted into the carpus before the little finger, and flexes the wrist. Protruding thus, this line runs along the lower surface of the ulna beyond the midpoint of its length; two others are seen besides this one; together with the one already mentioned, these shape the ulna, so as it proceeds from the humerus toward the wrist it appears not round but triangular. The second protruding line (b, b, in figs. 1, 2, 5) [margo anterior] runs straight down from the interior side of the root of the anterior process [p. coronoideus] of the ulna; with the first line, it forms a common side (d in figs. 1, 6) [facies medialis] which is impressed by the muscle which we just now said flexes the wrist. It [margo posterior] forms still another side (e in figs. 2, 6) [facies posterior] with the third line (c, c in figs. 1, 2, 5) [margo interosseus] which is the sharpest and roughest of the three and proceeds the farthest, from the outer side of the root of the ulna’s anterior process; it is produced and stands out so as to put forth a powerful ligament (V in the 7th table of muscles) [membrana interossea antebrachii] which connects the radius to the ulna along the length of the forearm like a strong membrane. The side (f in figs. 1, 5) [facies anterior] between the second and the third line is compressed for the sake of the muscles that occupy the inner part of the forearm, and for which a fitting place is provided here by the ulna and the radius. Chief of these muscles is the one [m. flexor digitorum profundus] (C in the 6th table of muscles) which you shall hear flexes the third of the four joints of the fingers. But since those muscles in their progress along the ulna also take a portion of their origin there, this third side lying between the second and third lines is rougher than the side seen between the second line and the first where no muscle originates except next to the joint of the ulna with the humerus where the muscle [m. pronator teres] (Q in the 7th table of muscles) originates which is the superior of those which pronate the radius. The side [facies posterior] bordered by the third and first lines is less compressed than the other two and has its own obtuse line (g, g in figs. 2 and 6), but that is long and not very prominent, running closer to the third line than the first. Nature produced it for the sake of three muscles (L, C, P in the 10th table of muscles) which take their beginning from this triple origin. The first [m. supinator] is the muscle that will be considered the shorter of those supinating the radius; the second and third serve the motions of the thumb and index finger, 45 as we shall explain in the second book. You will more easily understand it the more carefully you see in the bones what we are now saying. They are no less pleasant to see and know than the dissection of the brain and other parts which today we only marvel at. Though for the present I shall say nothing about the highest usefulness in the activities of our craft, so long as we keep our eye on these lines we will have the most certain knowledge that we have correctly repaired a fractured or dislocated bone. This is what the ulna is like well beyond the midpoint of its length. But closer to the wrist it would be quite smoothly rounded were it not that a second line protrudes noticeably at that point (b in figs. 1 and 5) and extending downward in a curve, makes ready a spot for the quadrangular muscle [m. pronator quadratus] (X in the 7th table of muscles) which we shall explain pronates the radius and takes its origin here. If anything remains to be explained about the ulna, I shall presently go over it


page 113

in my account of the radius, which is curved where the ulna is straight.



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