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 23 On the Humerus or Arm Bone

Description of the middle parts of the humerus

We shall perhaps pursue these matters at greater length elsewhere, but now we return to the remaining parts of the humerus, which are more or less smoothly rounded along its length, but wider and concave on the posterior surface more than on the anterior. The middle of the anterior surface [margo anterior] (b in fig. 1) protrudes longitudinally after a fashion, and on each side [facies anterior lateralis] [facies anterior medialis] (a and c in fig. 1) this anterior surface is compressed, while the sides of the humerus [margo medialis, m. lateralis], like the middle of the anterior surface [margo anterior], are observed to protrude rather than compress. All of this is because of the surrounding muscles, which, when you have understood their nature, will seem to have elegantly compressed the bone of their own volition. In addition, on the posterior side of the humerus near the middle of its length (Y in fig. 2), there appears a certain compression [sulcus nervi radialis] to which the fourth of the nerves [n. radialis] going to the arm 36 (F in figs. 2 and 3, ch. 10, Bk. 4) runs posteriorly from the inner [medial] side of the brachium obliquely downward toward the outer [lateral] side. But how the anterior and exterior [margo lateralis] surfaces of the humerus seemed convex to Galen in his book De ossibus 37 and the posterior [facies posterior] and interior [margo medialis] seemed concave, and why he declared in the second book of De usu partium 38 that the humerus was convex on the outside but concave on the inside, I do not comprehend. For unless we have established that the humerus is straight, it will be thought convex on its anterior and superior portion [crista tuberculi minoris] (d in fig. 1) but concave on its posterior and superior (X in fig. 2), and again concave in its anterior and inferior part (b in fig. 1) and convex in its posterior and inferior (Z in fig. 2). Then, unless I am mistaken, the interior, particularly toward the inferior, would be convex and the exterior concave. This is the shape that the muscles which bring about flexion and extension of the forearm 39 most of all induce, though there be less obliquity of the humerus than should cause disagreement. The roughness [tuberositas deltoidea] (e in figs. 1 and 2) which is in the anterior surface of the humerus towards the outside above the middle of its longitude is provided to insure here a stronger insertion for the muscles [m. deltoideus] that move the arm, and so that the posterior (G and then L in the 8th table of muscles) of the muscles [m. brachialis] that flex the forearm may take from here a suitable origin. This roughness is so great that in the elderly a notable process may be seen to arise here, provided chiefly for the insertion of the muscle that raises the arm [m. deltoideus] (D in the 10th table of muscles, then P in the 11th). Besides this roughness, another [crista tuberculi majoris] (f in fig. 1) occurs next to the depression [sulcus intertubercularis] in which the outer head of the muscle [m. biceps brachii, caput longum] is carried which is the anterior of those flexing the forearm; the fleshy part (o in the 6th table of muscles, where Q marks the muscle) of its interior head [m. biceps brachii, caput breve] will be shown to attach to this roughness. No noteworthy foramina occur in the humerus except a few near the brows of the depressions and heads, placed there so that ligaments might be more strongly brought from here, or implanted. There are also a few widely scattered foramina visible along the humerus cut particularly in its inner side (where the greatest number of vessels are carried) to admit veins; these extend into the wide cavity (inserted in the head, fig. 1) provided to contain the marrow and lighten the bone.



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 23 On the Humerus or Arm Bone