[Figures of Chapter 24]

Figure 1: This figure represents the two bones of the left forearm, shown in its anterior aspect. ¹ The fact that in this and nearly all the subsequent figures of this chapter the bones of the left side are seen but elsewhere as a rule the bones of the right side will be explained rather than the left, happens by chance because in the wood blocks we represented right for left. But in the bones it makes no difference whether the right or the left is presented.

What the ten figures that we have placed in order beneath the first figure of this chapter represent, and index of all the characters inscribed on the eleven figures.
In the second figure of the 24th chapter, both bones of the forearm, the radius and ulna, are shown in their outer [posterior] aspect. In the third, the radius alone is drawn on its inner [anterior] side; in the fourth, the radius on its outer [posterior] side. The fifth represents the inner [anterior] side of the ulna, the sixth the outer [posterior]. The seventh shows the lower [distal] portion of the right radius to which the carpus ² is articulated. We have drawn this part as if from below, the side facing the ulna, so as to keep in view the depression [incisura ulnaris] where the tubercle or head of the ulna [caput ulnae] is received here next to the wrist. The eighth figure, like the three after it and the first six, belongs to the left ³ forearm; it shows the lower part of the radius in its exterior aspect [facies posterior], so drawn as to reveal the depression [facies articularis carpalis] into which the carpus is articulated. The ninth illustrates the upper part [caput radii] of the radius, in which is seen the socket [fovea articularis] which the outer head of the humerus [capitulum humeri] enters. The tenth represents the lower portion of the ulna [caput ulnae], illustrating the part [circumferentia articularis] that faces the carpus. The eleventh shows the upper part of the ulna where the depressions, protuberances, and processes occur in which the groove or trochlea of the humerus is fitted.

The forearm
The entire part (A, B in figs. 1 and 2; T, V in the skeletal figs.) [antebrachium] between the humerus and the carpus is called ph/xuj by the Greeks and cubitus by the Latins. It consists of two bones that rest upon each other and are articulated together; the lower (all of fig. 5 and 6, or Y in the second skeletal fig.) [ulna], which is also the longer, is also called ph/xuj and cubitus.

Ulna and radius
Lest the homonymy obscure our account, whenever we mention this structure of two bones with its ligaments, veins, arteries, nerves, membranes, and skin, we have judged it best to use the word cubitus or forearm [antebrachium], and we shall call the lower bone the ulna and the upper ¹⁹ (all of figs. 3 and 4, or X in the second skeletal fig.) the radius throughout our account — as we have already been distinguishing them. These two bones are long, and they are different from each other nearly everywhere.

Articulation of ulna to humerus: description of its depression and processes at this point
In the first place, they are attached to the lower end of the humerus by altogether different types of joint. ²⁰ The ulna is articulated to the groove or trochlea (K, L, M of figs. 1 and 2, ch. 23) by depressions ²¹ carved to fit this purpose, and by suitable processes. On its upper end where it is quite thick and solid and like the lower end of the humerus has no epiphysis, ²² it has two conspicuous processes, one of which is prior or anterior to the other (the anterior is C [proc. coronoideus] the posterior D [olecranon] in figs. 1, 2, 5, 11). The anterior is the one that faces the depression (N in fig. 1, ch. 23) [fossa coronoidea] carved in the anterior surface of the humerus next to the upper region of the trochlea, and with its projections it exactly fits that depression. This process is wide,

Articulation of the radius to the humerus
That is how the ulna is articulated with the humerus; but where the radius is joined to the humerus, it is quite thin, and from a long, thin neck (M in figs. 3, 4, 9) [collum radii] it spreads into a wide, rounded capitulum (N in the same figs.) which forms, in the area facing the humerus, a circular depression (O in fig. 9) [fovea articularis] that is not very deep, which the head of the humerus ³⁴ (P in fig. 1, ch. 23) [capitulum humeri] enters. Upon this head the radius pronates and supinates, ³⁵ and does nothing to limit flexion of the elbow and extension of the joint of the radius with the humerus; ³⁶ indeed, the depression of the radius also flexes and extends on the head of the humerus. The length of the head of the humerus particularly helps such motion, as does its broad surface coated with cartilage, which never leaves the depression in the radius during motions of the forearm. Nature’s artifice is not to be neglected or overlooked: she so adapted the joint of the humerus with the radius that the radius and ulna can be flexed and extended, and at the same time the radius can be supinated and pronated while the ulna is not moving on the humerus.

The motion of the ulna on the wrist; its lower area
The ulna runs downward from its joint with the humerus more or less straight (from A to B in figs. 1 and 2) to the wrist, becoming gradually more slender and made constantly thinner until it reaches the carpus. It grows somewhat larger there out of its long, thin neck (P in figs. 1, 2, 5, 6, 10), and it has an epiphysis (Q in the same figs.) which is round like a head but irregular. It has a process (R in the same figs.) in its lower part which, because it goes to a point, the Greek anatomists call graphoid, grafoeidh/j, and styloid, stuloeidh/j, for its resemblance to a writer’s stylus. ³⁷ It is formed to augment the depression by which we shall explain the carpus is articulated to the forearm, and to provide an origin for the ligament (i in the 12th table of muscles) [lig. collaterale carpi ulnare] that holds the joint together. We shall address the use of this process in greater detail a little later, if only because Galen assigns too much to it. The lower part of the epiphysis of the ulna facing the carpus has an uneven depression ³⁸ at the inner side of the acute process (S in fig. 10) in which is braced the cartilage (T in figs. 1-4, 7-8) [discus articularis] which you will learn originates in the radius and is lodged mainly between the ulna and the carpus in such a way that it is attached to neither the carpus nor the ulna and is that type of cartilage [cartilago fibrosa] which we have stated (in the margin of chapter 10) is contained specially in the joints of the lower maxilla to the upper [articulatio temporormandibularis] and in the joint of the clavicles with the adjacent bones (R, S in fig. 4, ch. 22) [art. acromioclavicularis, art. sternoclavicularis]. Except for that depression in the epiphysis of the ulna, ³⁹ the entire area facing the wrist ⁴⁰ is coated with cartilage in the same way as the heads and sockets of all joints are covered and smoothed. In addition to this depression, the epiphysis of the ulna has a depression ⁴¹ (V in figs. 2 and 10) carved in its outer surface; this is long and (so to speak) smoothly rounded, having been provided for the tendon of the muscle inserted in the metacarpal ⁴² bone in front of the little finger [basis metacarpalis digiti quinti]; it is held to be an extensor of the carpus (L in the 9th table of muscles). But in addition to this epiphysis, the form of the ulna along its length and certain impressions and linear bulges still require consideration.

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

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

Articulation of the radius to the ulna
The radius is articulated to the ulna above and below by a very different joint: above, the ulna receives the radius, while below the ulna is received by the radius. So at the outer side of the anterior process of the ulna next to the humerus, a depression [incisura radialis] (l in figs, 5, 11) is carved transversely, resembling a quarter of a circle, smooth and coated with cartilage. The inner side (m in figs. 3, 4, 9) [circumferentia articularis] of the head of the radius in which a socket is carved that receives the outer head of the humerus [condylus humeri, capitulum h.], closely fits this depression [incisura radialis], and being smooth and round here, it revolves in this depression. But down below next to the wrist, where the radius thickens, widens, and has a large epiphysis (n in figs. 1, 3; this epiphysis is also visible in other illustrations of the radius), a depression is carved in the lowest part (o in fig. 7) [incisura ulnaris] of the epiphysis, not unlike the one which we said a little earlier is cut in the ulna. Into this depression coated with cartilage the upper part of the epiphysis of the ulna [caput ulnae, circumferentia articularis] (p in figs. 5, 10), protruding like a capitulum and covered with cartilage, rotates, and by this means the radius is pronated and supinated by the two joints. ⁴⁷

Smooth and rough surfaces on the length of the radius
Not far from the upper joint, where the neck (M in figs. 1-4, 9) of the radius is located, the radius puts forth a rough, blunt process (q in the same figs.) which faces the inner part of the forearm and provides a suitable place for insertion of the anterior of the muscles [m. biceps brachii] that flex the forearm. Moreover, in the remaining distance from the humerus to the wrist, the radius is not at all round and smooth. Along its lower portion it produces a sharp and quite prominent line [margo interosseus] (r, r, in figs. 1-4) which faces the third line [margo interosseus] of the ulna and admits the ligament [membrana interossea antebrachii] (T, V, S in the 7th table of muscles) that binds together both bones of the forearm like a very strong membrane where they stand apart. The outer side [facies anterior] of this line (s, s in figs. 1, 3), like the inner [facies posterior] (t, t in figs. 3, 4), ⁴⁸ is also compressed and concave to make room for the muscles occupying the outer and inner portions of the forearm respectively. The inner side is rougher than the outer, because the muscle [m. flexor pollicis longus] that flexes the third bone of the thumb (h in the 6th table of muscles) takes a major portion of its origin from that side. The upper area of the radius opposite the line just described is nearly smooth and round, and near the midpoint of its length it is somewhat rough (u in figs. 2, 3, 4) so that two muscles can achieve a stronger insertion: one of them [m. supinator] (Q in the 7th table of muscles) is the shorter of the ones that supinate the radius, the other [m. pronator teres] (L in the 12th table of muscles, and then d, e) ⁴⁹ the superior of those that pronate the radius. This roughness is particularly carved for the latter of these muscles because it makes a more sinewy than fleshy insertion ⁵⁰ and it runs further along the bone.

Account of the lower part of the radius
On the surface of the radius (all of figs. 7 and 8) adjacent to the wrist, which we have said widens and thickens, several things call for exact scrutiny. First, this part had to be enlarged to establish a satisfactory surface for the articulation of the carpus (1, 2, 3 in the first five figs. of ch. 25); ⁵¹ for it was necessary that the joint of the wrist with the forearm in humans be assigned a little less than completely on the radius ⁵² if when the ulna is stationary with respect to the humerus the hand was to be pronated and supinatedwith the benefit and aid of the radius. If equal portions were carved in the depressions of the radius and ulna to which the carpus is articulated, and the resulting articular cavity that matches the upper surface of the carpus had as the inevitable result to be transversely oblong, it would obviously have been impossible for both the radius and the hand to be pronated and supinated when the ulna was stationary on the humerus and performing as if it were the base and fulcrum of this motion. The part of the carpus which is inserted or articulated into the depression of the ulna would be in the way like a nail, preventing the radius from moving at all if the ulna did not move. For this reason it was worthwhile to thicken the lower part of the radius so that it would be suitable to make a socket to which the carpus could be articulated. But since it was not expedient to thicken a thin bone too much, Nature wished also that a portion be supported by the ulna, but in such a way that the ulna make contact with the carpus at scarcely more than a point. This contact is made by a sharp process [p. styloideus] (R in figs. 1, 2) which anatomists liken to a stylus.

Cartilage separating the carpus from the ulna
Lest the ulna touch the wrist with the rest of its epiphysis without the intervention of another body, Nature extended cartilage [discus articularis] (T in figs. 1-4, 7-8) from the lower surface of the depression (x, y, z in fig. 8) carved in the epiphysis of the radius for the sake of the carpus. This cartilage ascends the epiphysis of the ulna, separating it from the carpus, and so prepares the joint that the ulna indeed supports the carpus without coming into close contact, and the whole depression (as was quite necessary) faces the 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