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 27 On the Digits of the Hand

Appendix: the 1555 version of Chapter XXVII

(See note 13 above) For Nature herself had no less a rationale for the number and magnitude of the finger bones than for all of them together, which we see are rightly constructed in sets of five because of the tasks we perform with them, with four placed together in a row and a single large one more or less opposed to them to act as a kind of deputy hand, promanus (whence it is called a)nti/xeir by the Greeks 54 and by us pollex because of its strength). Similarly we see the fingers differ from each other in size and strength, and they differ in their functions. We perceive why they are unequal in length whenever we grasp a round object or when we put the fingers together and hold water or something of that sort, or hold them together and straight and forcefully thrust them at something.

The shape of the fingers taken together

We will the better judge the function of the hands with a single dissection the more it is realized that the bones of the fingers do not have at all the same shape as the complete fingers when still covered with skin and nails and possessed of the somewhat hard adipose tissue filled with nerves [nn. digitales palmares proprii] in the sides of the fingers and the larger number still in the internal areas beneath the skin. 55 Complete fingers are shaped a little less than completely round because such a shape, protruding in various ways but with no eminences, is less vulnerable to injuries. They are not as perfectly and exactly rounded on the inner side [palmaris] as on the outer [dorsalis] because some provision for resisting injury was necessary only on the outside, while on the inside the fingers knead, rub, and grasp; all of which they would do less well if they were smooth here. Moreover, since the fingers are less exposed to injuries in their sides, and being drawn together need for various reasons to be tightened and leave no empty space between them, it was in no way useful that they be smoothly rounded on the sides. Whence even the thumb has both sides smooth, and the inside more so, while the little finger has only its outside smooth but the index finger has its inside smooth, because these are the surfaces on which those fingers do not touch others, and they more or less resemble the outer surface of the fingers as far as repelling injuries is concerned.

In what way the finger bones differ from intact fingers above and below, and of what kind their substance consists

No bone of the fingers presents itself which is not thicker above and below [proximally and distally] than along its length, a common feature that is observed in almost all long bones, always thickening and growing toward the articulation. For if they were everywhere of the same thickness as they are at the joints, they would quite encumber a person with their weight and mass; and the joints themselves, if not proportionally fitted to wider bases, and not increased more than the bones elsewhere // p. 150 // along their length, would be quite weak. For this reason, although the bones of the fingers are hard and dense, they are not entirely lacking in marrow (look for these in bones that have been broken in various ways), as Galen believes. 56 For besides the fact that some of the epiphyses at either end are somewhat spongy, each also has a rather large cavity provided to hold marrow, as also in the metacarpal bones.

Design of the joints by which the finger bones are attached to each other and to adjacent bones

I shall now attempt to explain by what shape of joints the finger bones are articulated, and describe in each case what appearance they present throughout their length. The surface (G in figs. 3, 6, ch. 25) of the fifth carpal bone [os trapezium] (5 in the figs. of ch. 25), which is coated with smooth, slippery cartilage [cartilago articularis] for the first joint of the thumb [art. carpometacarpalis pollicis], projects transversely in a wide, elongated tuberosity (a to b in fig. 6, ch. 25), and is hollowed before (c in the same fig.) and behind (d in the same fig.) — but much more in front.

Attachment of the first bone of the thumb to the carpus

The first bone [os metacarpale 1] (A in figs. 1, 2, ch. 25) of the thumb is incised with a long, wide depression running transversely as seen from above or toward the outside if seen from the palm, 57 and it is convex anteriorly [distally] and posteriorly [proximally] (but more anteriorly), corresponding by mutual entry with the surface of the fifth carpal bone [os trapezium] just mentioned. The depression is not, however, so pronounced that this joint is moved in only one way; the same is true as a rule of the other joints that are brought together in this way. Though it is particularly capable of the lateral motion by which we move the thumb toward the index finger and back away again, and the joint appears to have been constructed especially for that motion, nevertheless it flexes and extends to some degree, and its flexion exceeds its extension by as much as the joint itself can be projected into the anterior side of the hand, or the palm, farther than into the posterior or outer side. 58

How the first bone of the thumb is articulated to the second

The first bone [os metacarpale 1] of the thumb is articulated [art. metacarpophalangealis] after a fashion to the second [phalanx proximalis] (this joint sometimes resembles C and D in the first fig.); its lower [distal] part ends in a single head, entering a single, simple depression of the second bone. But this head is not altogether round, nor is it equally pressed into a circle on every side. On its posterior surface and still more on its sides, it swells out nearly as much as the tip of its middle region, and only where it is brought out to the middle is it depressed, covered and fitted with cartilage for the second bone of the thumb. Over that head we flex the thumb more than we extend it or move it laterally. 59

How the second is articulated to the third

The third joint [art. interphalangealis] (this one exactly resembles the second fig.) of the thumb differs considerably from both the first and the second in the type of construction: the lower [distal] part of the second bone [phalanx proximalis] is divided into two oblong capitula running from the outside inwards, separately projected and rounded. They are separated by an elongated depression no less coated with cartilage than the capitula themselves, extending more into the inside than to the outside. The upper [proximal] surface [basis phalangis] of the third bone [phalanx distalis] has two depressions (I, K in fig. 2) separated by an elongated prominence (M in fig. 2); these receive the two capitula [caput phalangis] of the second bone, while the prominence of the third bone enters the depression of the second between its two capitula. In this way the second bone enters into the third and in turn receives the third, and both bones are so joined by mutual entry, and so cleverly, that the third bone can only be extended and flexed but in no way moved laterally, even in the smallest way. But because the capitula of the second bone extend with their depression to the inside as we just stated, the third bone flexes into an angle but extends from its flexion only to an erect position, not beyond a straight line in well articulated men. 60

How the second and third joints of the four fingers are articulated

The second (G and H into I and K and M into L in fig. 2) and third (as in fig. 3) joints [articulationes interphalangeales] of the remaining fingers are constructed with an altogether similar type of articulation, and experience only acute flexion and erect extension without any motion to the sides.

How the first of these is articulated

The first joint [art. metacarpophalangis] (A with B in fig. 1) of the four fingers is made with a single head [caput phalangis] (C in fig. 1) and a single depression (D in fig. 1). The metacarpal bones end in a single head that is much longer from the outside to the inside than from one side to the other, being transversely wide and substantial. This head extends much farther to the inside of the hand than to the outside, and is coated over a longer interval there with cartilage. But the depression // p. 151 // carved in the upper [proximal] end of the first bone of the four fingers is quite round, and the first bone is flexed, extended, and moved to either side above that head. But it is not, because of the shape of the head, which we said was oblong, rotated. The extension of this joint and its lateral motions are not as pronounced as its flexion; it does not make as sharp angles because the heads of the metacarpals are so slightly depressed on the outside and to the sides. But the farther this head is covered with cartilage to the outside than the heads of the second and third joints, the farther the first joints can be extended beyond a straight line than the second and third. In the same way, the index finger [digitus secundus] can be inclined to the inside [medially] and the little finger to the outside [laterally] more than the other fingers because the heads of their first joint are extended on those sides and widened as if into a circle to such a degree that the unique purposefulness of Nature occurs everywhere, making such careful provision for the strength of the parts that she did not want the first joints to rotate, since the pronating and supinating motions of the hand and the radius abundantly provide for the rotation of the fingers.

Nature’s purposes in the joints of the fingers

As those motions, together with the rotation of the humerus on the scapula, make an equal flexion and extension of the fingers unnecessary for us, so because we are able to move the first joints of the fingers laterally there is no need for the second and third joints to be built so loosely that they are capable of the same motion. And so it is that the more diligently I ponder these things that present one artifice of Nature hard upon another, the more I wonder why Galen categorized all the finger joints as having a more or less mutual entry in his book On the Use of the Parts, 61 and in his book On the Bones 62 he attributes the same type of joint to all the bones when he says that the head of the upper bone enters the depression of the one that follows, no differently than if he had thought that all joints are brought together in the same articulation. Then in his books On Anatomical Procedures he so composed his account of the muscles in all respect contrary to the views of the ancients that he assigns tendons that move the fingers laterally [abduction] no less to the second and third finger bones than to the first. 63 However this may be, even in their system of articulation the bones of the fingers vary considerable from the appearance of intact fingers.

The extremity and tip of the third finger bone

In addition, the third bone also protrudes in its lower surface [tuberositas phalangis distalis] (the tips in figs. 1,2, ch. 25) where it is not attached to any bone, and has a rough capitulum with two vinculum-like connections so that a tendon (q of muscle h and g of muscle C) 64 is attached to the entire inner surface of this bone [phalanx distalis] which flexes it and is at last very strongly inserted at its end as if into the tip of the bone, which is somewhat cartilaginous at its extremity. For the sake of this tendon (compare the first fig. of ch. 25 with the second, and the bones with each other), the third bone [phalanx distalis] is rough and irregular on its entire lower surface, where it protrudes slightly.

The inner surface of the bones along their longitude

Along its longitude, the inner surface of the first bone of the thumb resembles the inner surface of the metacarpals, which projects a little more sharply than a rounded shape. But the first bones of the four fingers, and the second bones as well as the second bone of the thumb, are depressed and more concave with a flat surface than convex in the entire region visible between their joints; this is for the tendons 65 that are extended upon them, which because they are smooth and round could not have rested upon a body that is also smooth and round. Indeed, not only are such tendons extended along those bones, but ligaments also are brought from the bones, on which tendons run as if on rings 66 by which they are held against the depressed surface of the bones and are not allowed to rise up from them. There is situated on the second bone [phalanx proximalis] of the thumb a tendon [m. flexor pollicis longus, tendo] (q of muscle h in the 6th table of muscles) that flexes its third bone [phalanx distalis]; and in the first bones of the four fingers two tendons present themselves, of which one [m. flexor digitorum superficialis, tendo] (o of muscle Q in the 5th table of muscles and d of muscle e in the 6th) flexes the second bone of the finger and the other [m. flexor digitorum profundus, tendo] (g of muscle C in the 6th table of muscles) flexes the third; it is also brought down from the second bone, though no such tendon is attached to the first bone of the thumb, which like the metacarpal bones is wide on its outer side and more depressed than convex. But the outer surfaces of the remaining finger bones are quite convex and smooth, and on these surfaces widely expanded tendons [m. extensor digitorum, tendines] (of muscles Z, Q, f in the 9th table of muscles) like membranes are inserted; no round tendons are carried on these surfaces. Now the third // p. 152 // finger bones, though they are smoothly rounded on the outside, from the articulation by which they are joined to the second bones to their extremity are not as convex as the rest. But as they make way for the nails they are less protuberant proportionally to how much space the nails occupy, lest the entire finger rise higher over the third bone than over the others.

The sides

The sides of the first bone of the thumb, like those of the third bones, are more or less smoothly rounded. The sides of the first bones that are in the four fingers and of the second bones of the five fingers resemble the side of the half that would be cut through the middle from a rounded body; for such bones would need to be flat on the inside and convex on the outside. The sides of the bones of the thumb, index finger, and little finger are in no way exceptional at this point (like the whole fingers at other points). Thus Galen may be seen wrongly to declare that the form of the intact fingers and that of their bones is identical.

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 27 On the Digits of the Hand