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

Index of Characters in the Two Figures of the Present Chapter

A, B, C, D, E, F, G, H Some of these letters are to be found in the first figure, others in the second, indicating the epiphysis 1 of the humerus which is quite complexly shaped, as I shall show.
A, B, C[ 1 , 2 ] In both figures these letters circumscribe the head of the humerus [caput humeri] which is articulated into the scapula.
D, E[ 1 , 2 ] Both letters are seen in the first figure, marking the outer head [tuberculum minus (D), tuberculum majus (E)] of the epiphysis of the humerus,

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into which the ligaments of the joint [articulatio glenohumeralis] are inserted. D marks the anterior [facies anterior] head of this outer head, E the posterior [facies posterior], which is more visible in the second figure than in the first.
F, G[ 1 , 2 ] These two letters in the first figure, and G in the second, mark the broad depression [collum anatomicum] that separates the inner head from the outer. We shall add the rest of the index beneath the figures to be placed here. 2

First figure of the twenty-third chapter, showing the anterior face of the right humerus.

Second figure of this chapter, setting forth the posterior face of the right humerus.
H, I 1 Depression [sulcus intertubercularis] dividing the outer head in two, provided for the outer head of the anterior of the muscles [m. biceps brachii, caput longum] that flex the forearm.
K, L, M 1 , 2 Trochlea 3 [condylus humeri, trochlea humeri] of the humerus, against which the ulna is flexed and extended; K marks the depression [sulcus] of the trochlea, L and M the sides: L the internal side, M the external.
N 1 Depression [fossa coronoidea] incised at the upper part of the trochlea in the anterior surface of the humerus.
O 2 Depression [fossa olecrani] quite deeply hollowed out at the upper part of the trochlea, in the posterior side of the humerus.
P 1 , 2 Head or tuberculum [condylus humeri, capitulum humeri] of the humerus to which the radius is articulated. In the first figure of this chapter the part appears which is covered with cartilage. In the second, that part [epicondylus lateralis] appears to which the radius is not joined, but which serves elegantly for the origin of muscles. 4
Q 1 , 2 Here [crista supracondylaris lateralis] the humerus protrudes for a great extent of its length like a sharp line. 5
R 2 Depression [sulcus] in this outer head [epicondylus lateralis] of the humerus, carved out for the fourth of the nerves 6 going to the arm.
S 1 , 2 Inner tubercle [epicondylus medialis] of the humerus. 7
T 1 Depression in the anterior of the tuberculum, provided for the third of the nerves going to the arm.
V 2 Depression [sulculus nervi ulnaris] in the interior tuberculum, in which the fifth nerve [n. ulnaris] to the arm is carried.
X, Y, Z 2 Posterior area [facies posterior] of the humerus. X marks the superior portion, which is concave; Z marks the inferior part, which is convex; Y marks the impressed place [sulcus nervi radialis] on which the fourth of the nerves [n.radialis] to the arm is turned.
a, b, c, d 1 Anterior area of the humerus, where b [margo anterior] identifies its prominent or convex part, a [facies anterior lateralis] and c [facies anterior medialis] the place where the bone is depressed on each side near this protuberance. These three letters together mark the concave lower part of the anterior side of the humerus; d [crista tuberculi minoris] marks the upper area, which is convex.
e 1 , 2 Roughness [tuberositas deltoidea] located next to the outer side of the anterior part of the humerus. 8
f 1 Roughness [crista tuberculi majoris] visible in the anterior part of the humerus, at the root of the depression [I] that brings out the outer head of the muscle [ m. biceps brachii, caput longum] which is considered the anterior of those that flex the forearm. 9

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Humerus and Brachium
The bone which is articulated to the scapula and the lower arm (S to R and T, V in the skeletons) is called the humerus by Celsus and many others, braxi/wn by the Greeks (and very many Latin authors). In our account to distinguish the whole bulk of bone and muscles, nerves, veins, arteries, skin, and whatever else goes into the construction of the arm from the bone itself, when referring only to the bone we shall call it the humerus, or sometimes the brachial bone. But when we refer to the other parts of the limb together with the bone, we will use the word brachium, not unfittingly in the interest of clear exposition.

The humerus is not larger than all the bones after the femur, as Galen believes.
In Galen’s opinion, 10 the humerus is the largest of all the bones of the body with the sole exception of the femur; but one grants that the fibula and the tibia significantly excel the humerus in length. Moreover, the tibia surpasses it in thickness and weight just as the bones articulated to the sides of the sacrum far surpass the humerus in weight. 11 Thus we can think of several bones besides the femur to which the humerus yields in magnitude. But on this point and a great many others we shall yield to the authority of Galen, since others will not permit us to oppose his opinions. 12

Description of the upper part of the humerus
The highest part [pars proximalis] of the humerus, where it is articulated to the scapula, has a very large epiphysis (A, B, F, H in fig. 1) which is split into two heads. This epiphysis forms on its inner side a wide (A, B, C in figs. 1 and 2), round head [caput humeri] which protrudes a little less than a hemisphere and is smooth and regular; it is coated with cartilage and articulates with a depression [cavitas glenoidalis] of the scapula (A, B in fig. 2, ch.r 21). This head constitutes the inner side of the epiphysis and occupies somewhat more than half of its upper region. The outer side of the epiphysis protrudes after a fashion to form another head [tuberculum minus, t. majus] (D in fig. 1, E in figs. 1, 2), rough and irregular, which is not indeed erect for some joint, but rises only like a hill into which many strong ligaments [ll. capsularia] that bind the humerus to the scapula are implanted. On the outer side of the inner head [caput humeri] , which is on a rather prominent point, the highest on the epiphysis, and then on the anterior and posterior portion of the same head, a wide and spreading depression [collum anatomicum] (G, F in fig. 1, G in fig. 2) runs in a circle, separating the inner head (which serves for articulation) from the outer [tubercula] (which is adapted for receiving ligaments) and providing a suitable place for the insertion of ligaments [ll. glenohumeralia, l. coracohumerale]. For ligaments are inserted into this circular depression which spreads and becomes wide and deep like a valley more in the anterior portion of the humerus than in the posterior. Ligaments make their insertion into the outer head, which is distinguished from the inner by this depression, as if into a hill or some promontory. And just as the points in all bones where something is inserted or from which something takes its origin are rough and uneven, so also the present depression and the outer head are rough and uneven. Besides the fact that this outer head protrudes unevenly and is irregular, it is again divided as if in two by a certain depression [sulcus intertubercularis] (H, I in fig. 1) into an anterior [tuberculum minus] (D in fig. 1) and a posterior [tuberculum majus] (E in figs. 1 and 2) which is much larger than the anterior. This depression, carved a little toward the exterior in the anterior part of the epiphysis, is quite deep, long, and smoothly rounded throughout, just like the body for which it is carved out, which is the outer head (the muscle is marked Q in the 6th table of muscles, the head m) of the anterior of the muscles [m. biceps brachii, caput longum] flexing the forearm. I believe no one will fail to see that I understand the depression following the muscle is concave and that the head following the convexity of the muscle is smoothly rounded, as long as it is understood that all depressions are hollow and things carried in them or lying therein are convex. 13 This long depression extends not only to the epiphysis but also to the part of the humerus (I in fig. 1) to which the epiphysis attaches, and which constitutes the very short, quite thick neck [collum chirugicum] of the humerus. This is how it is with the upper part of the humerus adjacent to the scapula. 14

Description of the lower part of the humerus
The lower part [pars distalis], which is articulated to the two bones in the forearm (the first four figures of the next chapter), to wit the ulna and the radius, is much more complicated in the number and appearance of depressions as well as its heads and protrusions. First, there is seen in the middle of the lower part of the humerus a depression (K, L, M in figs. 1 and 2) with its high points [condylus humeri, trochlea humeri] very much resembling the little wheel in a pulley on which ropes turn. As the wheel of a pulley is round and orbicular in circumference but smooth and wide on the sides; so on this end [pars distalis] of the humerus the round, orbicular part is seen which you will say resembles nothing so much as a little wheel. In its perimeter like a little wheel on which a cord is turned, it is carved out with a depression [sulcus] (so to speak) that is rounded, smooth, and slick; sides protrude on both sides of this depression as if to hold a rope and prevent it from slipping off: in such a way this part of the humerus is depressed in the middle and protrudes on each side. But it differs in this respect from the projections of a perfect pulley wheel, that the wheel’s sides are nearly always evenly raised above its depression. But this part of the humerus projects quite significantly on its inner side [facies medialis] (L in figs. 1, 2) and exactly resembles a pulley wheel, while on its outer side [facies lateralis] (M in figs. 1, 2) it is much less extended. 15 This is not to say that Nature was more inattentive than the makers of pulley wheels or less clever, but that it was not necessary for the depression of the humerus or the sides of its groove to be evenly extended everywhere. For as a pulley wheel that faces a frame 16 on one side can protrude

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less without harm on the side facing the frame than on the other (for there is no fear that the rope will slip off the wheel on the side that nearly touches the frame), so too the outer side of the humeral trochlea is not as endangered as the inner. For we shall soon add that there is another head [condylus humeri, capitulum humeri] (P in figs. 1 and 2) near the outer side, to which the radius is articulated and which can be considered like a frame or wall preventing the ulna from being dislocated outward from its groove. But there is another difference between the trochlea of the humerus and an actual pulley wheel: the ulna cannot be moved around to every part of the trochlea as a rope can be moved on a pulley. For although the humerus is markedly depressed in the upper and middle area of its groove (N in fig. 1, O in fig. 2) and is extremely thin and transparent like a scale, 17 nevertheless it is not open, and that is for a very good reason. For when the supreme Maker of things desired the ulna to be flexed and extended on this groove [trochlea humeri] of the humerus, he so prepared the trochlea and bestowed depressions, protrusions, and processes (C [processus coronoideus], D, E [incisura trochlearis] in figs. 1 and 5, chapter 24) on the ulna itself that we are able to flex and extend the forearm without being deprived of strength in these motions. This would have been impossible had the humerus been open on the superior part of the trochlea and there were nothing on which the ulna could be braced in its furthest extension, and the trochlea were wrapped as by a rope without a stop, base, or obstacle. And so Nature carved out two notable depressions on the top of this trochlea, one [fossa coronoidea] (N in fig. 1) in the anterior part, and the other [fossa olecrani] (O in fig. 2) in the posterior, which is wider, deeper, and in one way or another more conspicuous than the anterior. These depressions, separated only by a kind of scale, receive the processes of the ulna (which they specifically name korw/nai). The anterior depression admits the anterior [processus coronoideus] of these processes when the forearm is flexed; and when the forearm is extended, the posterior depression receives the posterior process [olecranion] of the ulna. These depressions have been made the limits of extreme flexion and extension with such foresight that they allow the forearm to be flexed to a very sharp angle and permit it to be extended not much beyond a straight line, because we clearly have no need at all of extension to an angle as we certainly do for flexion. 18 Now because the depressions of which we are speaking are like bases and obstacles in the motions of the forearm that do not let the ulna be taken too far, Hippocrates called them baqmi/dej, and the trochlea gigglimoeidh/j from its resemblance to a hinge. 19 We will correctly understand the use of these depressions when we complete the description of the ulna in the next chapter. For the present, however, we must continue our description of the lower end of the humerus. 20 At the extreme edge of the trochlea of the humerus there is a rounded and somewhat oblong head [capitulum humeri] (P in fig. 1), which like the groove is smooth and covered with cartilage; it serves the articulation of the radius with the humerus and enters the upper depression [caput radii, fovea articularis] (O in fig. 9, ch. 24) of the radius, and the radius (as I shall explain elsewhere at greater length) pronates and supinates on this head. 21 The length of this head, which I measure from its upper to its lower part along the length of the humerus, is the reason why in the flexion and extension of the forearm this head does not slip out or escape from the depression of the radius (which is round but not oblong). The entire part of the head that is covered with cartilage faces the anterior surface of the humerus and does not occur at all in the posterior, because the radius does not approach the back of the humerus in any extension of the forearm. But on the outer side of this head the humerus protrudes significantly [epicondylus lateralis] and looks like a mountain or a cliff; it is made this way so that as many muscles as possible may conveniently take their origin hence. From this part of the humerus 22 (P in fig. 2 towards Q [crista supracondylaris lateralis] in figs. 1 and 2 where the line is marked) and along a sharp line [margo lateralis] which ascends from this protrusion upward some distance along the outer side of the humerus, six muscles take their origin, 23 the first 24 of which (Q in the 12th table of muscles) [m. brachioradialis] may be counted that which is wider than the others; it is by far the longest among those that move and supinate the radius. The second (L in the 11th table of muscles) [mm. extensor carpi radialis longus et brevis], originating below it, extends the wrist by means of a two-horned tendon. The third (Z in the 9th table of muscles) [m. extensor digitorum] is the muscle by which the index, middle, and ring fingers are extended. The fourth (Q in the 9th table) [m. extensor digiti minimi] is the one which we make the chief author of extension of the little finger. The fifth (L in the 9th table) [m. extensor carpi ulnaris], extended along the ulna, is also responsible for extension of the wrist. The sixth 25 (m in the 11th table) [m. supinator] will be counted the second of the muscles that supinate the radius; a small part of it originates in its turn from the tubercle [epicondylus lateralis] of the humerus at its lowest end. Whenever mention is made of the muscles, nerves, veins, and arteries passing this point, we shall always call it the outer protrusion or tubercle of the humerus. It is, as we have stated, made for the origin of muscles, and on its posterior surface it forms a depression [sulcus] (R in fig. 2) next to the outer side (M in fig. 2) of the trochlea of the humerus where the fourth [n. radialis] (F in figs. 2 and 3, ch. 10, Bk. 4) of the nerves going to the arm is carried. 26 But just as this outer side of the humerus protrudes, so too the inner side has a conspicuous, sharp process or tubercle [epicondylus medialis] (S in figs. 1 and 2), also for the sake of muscles and nerves, but not protruding for the sake of any joint like the outer end [capitulum humeri] to which the radius is articulated. At the inner side (L in figs. 1 and 2) of the trochlea of the humerus a process [epicondylus medialis] comes out from whose tip, which is quite wide, a muscle [m. palmaris longus] (P in the 3rd table of muscles) originates which goes to the inner skin of the hand via a long tendon; next, two flexors [m. flexor carpi radialis, m. flexor carpi ulnaris] (L in the 3rd table of muscles) of the wrist. In addition, a portion of the muscle [m. pronator teres] (Q in the 7th table) that is considered the superior of the muscles that pronate the radius, also originate from the lowest part of this process (which we shall always call the inner tubercle of the humerus). Finally, an obscure portion of the beginning of certain muscles that flex the fingers (Q in the 5th table of muscles, C in the 6th) 27 hangs from this point. But

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this tubercle does not serve only for the origin of muscles; it also makes a suitable location for two nerves that go to the forearm and should be considered a bulwark for them. On its anterior surface next to the trochlea, it displays a lightly carved depression (T in fig. 1) 28 along which the third of the nerves [n. medianus] (t in fig. 2, ch. 10, Bk. 4) going to the arm is arranged. On its posterior surface, in another depresion [sulcus nervi ulnaris] (V in fig. 2), it brings down the fifth nerve [n. ulnaris] of the arm (* in fig. 2, ch. 10, Bk. 4). However large the inner tubercle [epicondylus medialis] of the humerus is (see the elbow joint in the skeletal figs.) and easily detected by touch and observed, we must not on this account believe Galen, 29 who stated it was larger than the outer tubercle [epicondylus lateralis], though the larger is much larger the inner; for because it does not present itself to touch as readily as the inner tubercle, it is not its size but the radius to which it is articulated that prevents it from being distinguished by touch. 30 In dogs, horses, sheep, and suchlike animals these protrusions of the humerus differ very little from this construction, except that the outer head of the humerus [capitulum humeri] that is articulated to the radius is less distinguishable from the outer side of the trochlea the more the radius is bound and connected in such animals with the ulna — more than in humans, whose radius is pronated and supinated quite clearly and is loosely articulated with the ulna.

The errors of Aristotle and many others
I have no doubt that the followers of Aristotle and those who have said anything about the motion of animals that depends on his opinion, found often in his works but especially in his work On the Common Movement of Animals 31 — among them Galen in the third book On the Use of the Parts, 32 Pliny, 33 and among many others our own Erasmus of Rotterdam in his insufficiently anatomical dialogue “On the Game of Knucklebones” 34 — that such persons will be more than a little astonished that I find so little difference between humans and quadrupeds in this part of the humerus, or in the joint of the humerus with the forearm; when at the same time (to omit other issues) Aristotle and as many as follow him describe a different flexion in ourselves and the quadrupeds when they teach that we perform this flexion forward and they do so backward. Not only is this false, but Aristotle also deprives quadrupeds of one bone, the humerus itself, believing that the joint of the humerus with the forearm occurs in them where the foreleg is joined with the carpus. This is a joint which those animals have in common with us, and they perform the same flexion as we do in the joint of the forearm with the humerus. Yet the humerus of those animals, as well as their femur and that of birds, was equally unnoticed by Aristotle, perhaps because it was hidden in the trunk of their body unlike our humerus and femur. 35

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]