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 1

[Figures of Chapter 27]

The two first figures at the beginning of the twenty-fifth chapter show the sequence of finger bones, as do the three tables illustrating the entire assembly of bones which are placed at the end of this Book. The illustration inserted here, broken down as it were into three figures (so that each presents two bones) presents to view the joints 2 of the fingers. The first of these represents two bones, one of which I have marked A ; it is the metacarpal bone [os metacarpale II] that supports the index finger [digitus secundus]. The other is marked B , and it is the first bone [phalanx proximalis] of the index finger drawn from the outside [prospectus dorsalis], as is the metacarpal bone. In this figure, a picture of the first joint [articulatio metacarpophalangealis] of the fingers is set forth. C marks the round head [caput metacarpale] of the metacarpal bone, D the depression [basis phalangis] of the first bone of the index finger that receives the head marked C. The second figure also shows the first bone of the index finger, marked E , and the second [phalanx media], marked F , in such a way that the drawing would illustrate the appearance of the second joint [art. interphalangealis] of the four fingers. G and H mark the two capitula [tuberositas phalangis distalis] of the first bone of the index finger. I and K mark the depressions [facies] of the second bone which the two heads [condyles] of the first bone enter, while L marks the depression that lies between the heads of the first bone, and into which the tubercle [dorsum] of the second bone, marked M , rising between the two depressions, labeled I and K, enters. The third figure represents the second bone of the index finger, marked N , and the third [phalanx distalis], marked O , so as to show the appearance of the third joint of each digit, which because it closely resembles the second joint of the four fingers we have not filled with other letters. It is also possible to look up pictures of these joints in the first two figures of the twenty-fifth chapter. 3

The fingers are rightly made up of three bones each
It was stated in the previous chapter that all the digits of the hand (in figs. 1 and 2, ch. 25, the bones of the thumb are marked A, B, C, those of the index finger D, E, F; the system applies also to the others) consist of three bones each 4 — they are called internodes, joints, and acies 5 , or also fa/laggoj, 6 skutali/dej, 7 and ko/nduloi. 8 These bones are hard and dense, but not entirely without marrow (as we have sometimes warned contrary to Galen’s view). 9 For besides the fact that they are somewhat spongy above and below like epiphyses, each has a rather large cavity provided to hold marrow as in the metacarpal bones. I believe it is no secret that we require the bones of the fingers for strength of action in grasping things, and we need many of them because of the various motions which the hands perform and the diversity of things which are grasped by them. 10 Next, it is very easily inferred that it was altogether practical for the fingers that there are neither more bones nor fewer than three, because if there were more than that number, not only

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would they serve no purpose (we all can do a great deal with three bones), they would also interfere with the complete and effective extension of the fingers, making it less strong than it is. For things constructed of more parts more readily become fatigued, tired, and deprived of their strength than those fashioned of fewer, chiefly because all the pieces, once joined and attached together (like the carpal bones), are unable to be maintained in all of their functions. But if the fingers were made up of fewer bones, we would be unable to move the fingers into such various and contrasting shapes. So the number of three bones is sufficient that they be moved in a number of ways and avoid a liabitity to be hurt.

The just size of the bones 11
Since it is worthwhile that a bone that comes before be larger than the one that comes after it, or the bearer than the one borne, Nature also rightly fashioned the first bone of each digit larger than the second, and the second in turn greater 12 than the third, reducing the lower bones not only in length but also in thickness and width, in this way chiefly constricting the fingers from a wider base gradually to a point and arranging a shape of the fingers which we consider most becoming in women. 13

The fitting shape of bones and entire fingers
But with amazing design she did not bestow the same shape on the finger bones as on the fingers when covered with nails and skin. She shaped the digits as a whole a little less than completely round because she knew such a shape to be less prone to injuries than any other, as naturally a shape without projections is least likely to be fractured or crushed by collisions with outside objects. Consider it done for some useful purpose that the fingers are precisely rounded on the outside [prospectus dorsalis] while inside [prospectus palmaris] and on the sides they are more compressed. In their inner region the fingers soften, knead, rub, and grasp: all of which they would do less well if the fingers were convex in that area. 14 I pass over the rather firm fatty tissue that is filled with sinews and stretched over the inner surface of the fingers for the functions I have just mentioned and to protect the tendons; 15 I shall discuss this at greater length in a separate chapter of the second Book. Furthermore, since we try to do none of these tasks or perform any other with the outside of the fingers, it was reasonable that they be made perfectly convex for durability only. But since the fingers are less exposed to damage on the sides, and needed to be drawn up against each other, held in, and to leave no empty space between themselves, it was not at all useful for them to be made convex on the sides. The thumb, little finger, and index finger give sufficient support to the purposes I have just mentioned if the thumb has either side 16 convex but especially the inside [ulnaris or pars medialis], while the little finger is convex only on the outside [ulnaris] and the index contrariwise has the inner side [radialis] convex, for on these sides they are not protected by another. In this way we see no small cleverness of Nature in the shape of the complete finger. I shall now endeavor to explain to what extent the bones diverge from this shape. (Keep an eye here on the figures in which the bones of the fingers are illustrated.) No finger bone can be found which is not thicker and denser at the upper and lower ends 17 than along its length; this is also commonly seen in virtually all the long bones, which constantly thicken and grow toward the articulation. 18 For if they were equally thick everywhere, they would considerably impair a creature with their weight and bulk, and the joints themselves, unless they were fitted with correspondingly larger bases, would be quite weak. It is in this respect first that the shape of the bones varies from that of the finger as a whole. If the finger imitated the shape of the bones along their sides, as can be seen in persons who are thin and emaciated, the space between the sides of the fingers would be empty, which would make it impossible for the fingers to hold a liquid, at no small inconvenience. This area of the bones is filled with the rather firm fatty tissue which we mentioned in passing a little earlier. 19 In addition, each bone of the finger is smooth and convex on its outer surface [prospectus dorsalis], protruding nowhere conspicuously beyond a straight line, even in the area of the joints, as even on the sides [radialis / ulnaris] the bones do not project very much around the joints. The exception is the first bone of the thumb [os metacarpale I], which on its outer surface is wide, more flat, and depressed, and does not seem convex like the others. The third bones of the fingers [ossa phalanges distales] are convex on the outside [prospectus dorsalis], but they run downward from the joint where they are articulated to the second bone [phalanx media] and do not bulge outward in the same way the other bones, but give way a little for the fingernail. They jut out less, proportionally to the space the fingernails occupy, no doubt so that the entire finger will not protrude outward farther at the third bone 20 than in the others. The inner side [prospectus palmaris] of each bone is much different from the outer surface [prospectus dorsalis] of the fingers, depressed or rather concave no less than the outer is convex; 21 but here too you should make an exception of the first bone of the thumb, which on its inner surface resembles the bones of the metacarpus. 22 For although it protrudes more above and below in the area of the joints into the internal area of the hand, and appears interiorly concave in the middle of its course but curved on the outside, still it is not wide, depressed, and level like the other bones of the fingers, but rather convex and more sharp inside [palmar] than outside [dorsal]. Nature devised this by no means randomly or by chance; for along the inner [palmar] part of the second and third bone of the thumb, as along the three bones of the four fingers, slender tendons 23 (see the hands in the 5th table of muscles as well as the 6th and 7th) needed to be extended, which unless the inner surface of the bones were wide, depressed, and more or less concave, would not have been able to remain in place, any more than we ever observe smoothly rounded bodies lie upon each other.

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Those smoothly rounded tendons needed not merely to be laid against the bones: it was worth the trouble also that a ligament [vaginae synoviales et fibrosae digitorum manus] (see the hand in the 4th table of muscles) originate from this place on the bones, attaching the tendons to those bones along their length and holding them together to prevent their rising from the bone or falling away. We shall provide a satisfactory explanation in the second Book what kind of tendons extend along the bones and what ligaments 24 cover them. For the present, it is enough to mention them only so much as suits an account of their relation to the structure of the bones. You will hear in that book that this kind of ligament originates along the length of the second bone of the thumb on its inner surface, accompanying the tendon of the muscle [m. flexor pollicis longus] (h and q in the 6th table of muscles) which is very strongly inserted in the third bone of the thumb and causes flexion of that joint. But because Nature placed no such ligament in the first bone of the thumb, and there was no danger that the tendon running this way to the third bone of the thumb would stray anywhere (since it is restrained on both sides (i [m. abductor pollicis brevis] in the 4th table of muscles, k and l in the 6th, and 1, 2, 3 in the 7th 25 ) by muscles peculiar to the first bone of the thumb), it was not at all necessary for the first bone of the thumb to be made flat and depressed on its inner [palmar] side like the other bones, especially since it was also unsuitable for the muscles extended along it and inserted into it. Along the four first [proximal] bones of the fingers are extended two tendons lying upon each other (g and d in the 6th table of muscles), one of which [m. flexor digitorum superficialis, tendines] is inserted into the second bone and the other [m. flexor digitorum profundus, tendines], which lies beneath, is implanted in the third; tendons of this kind are conveyed in this way to the three bones of these fingers, and the bones of the fingers are equipped with ligaments [vaginae synoviales et fibrosae digitorum manus] of the type which transmit tendons ring-fashion: especially the first and second bones of the four fingers and the second bone of the thumb. 26 Tendons are not extended along the third bones over their entire length, and for this reason they do not look as depressed and flat as the lower bones. 27 It was therefore reasonable that these bones are constructed no differently than if they were one half of a cylindrical body, while the tendons running along them were the other half of this body, so that the bones combined with the tendons would form the cylindrical shape of the finger. No such tendons are run to the outside part [proximalis dorsalis] of the fingers 28 (see the hand in the 9th table of muscles and some of those that follow): tendons are just attached there like a membrane along the complete length of the bones. 29 The sides of the bones are also not flat and compressed like the fingers, nor is there any difference in this area between the bones of the thumb, little finger and index finger, and the bones of the other fingers. The sides of the bones resemble the side of a cylindrical body cut in half, although the first bone of the thumb [os metacarpale I] differs to the extent that it is less wide and flattened on its inner side than the other finger bones. Such is the shape of the digital bones, certainly far different from the shape Galen attributed to them when he described them according to the shape of the fingers. 30

The system of articulation of the finger bones 31
But it would now be timely to consider the providence of Nature in the joints of the fingers, and not to acquiesce casually in Galen’s account where he pronounces in a simple way 32 that the head [caput phalangis] of the upper bone enters into the depression [basis phalangis] of the bone that follows, and that the outer [dorsal] rims of the depressions are extended or swell out more prominently than the inside [palmar] ones, 33 and when he attributes the same type of articulation to all the finger joints. This is to say nothing for the time being about the tendons (p, r in the 3rd table of muscles, z, z in the 6th, f, g in the 7th, C, P in the 10th, etc.) of the muscles which draw the fingers to the side 34 and are thought by Galen to be just as common to the second and third finger joints as they are to the first. 35 But we will now show with ease that neither the third joint of the thumb nor the second or the third joints of the other fingers are moved to the side by primary motion.

Attachment of the first thumb bone to the carpus
The first bone of the thumb [os metacarpale I] is joined to the fifth bone of the wrist [os trapezium] by a rare and peculiar type of joint (G, a, b, c, d in fig. 6, Ch. 25) [art. carpometacarpalis pollicis] that can be flexed and extended as well as moved to the sides; it is prepared in such a way that it provides separately more for motion that is performed to the sides than for flexion and extension. 36 The fifth carpal bone forms a broad depression that projects transversely in a rather wide extension and is carved out more visibly on the inner and outer surface than on the sides. The first bone of the thumb is carved out transversely, or between its inner and outer side, at its upper end [basis metacarpalis], and as it protrudes inside and out it elegantly fits the depression [facies articularis metacarpalis] of the fifth carpal bone, and articulates with it as if by mutual entry. But this is not so pronounced that it has but a single motion, like the mutual entry of other joints. Rather, since the inner surface [facies ulnaris] of the first bone of the thumb juts out more than the outer [facies radialis], and enters more deeply into the depression of the fifth carpal bone which is more deeply grooved at that point, the first thumb bone can be flexed more than extended.

The type of joint of the second thumb bone with the first, and its motions
The second bone of the thumb [phalanx proximalis] (see here C in fig. 1, which is inserted into D) is articulated with the first by that type of joint 37 which the Greeks call e)na/rqrwsij. 38 The lower part of the first thumb bone ends in something like a round capitulum [caput metacarpale] that enters the round cavity [basis phalangis] of the second bone. But because this head protrudes transversely, i.e., from the inner side of the thumb more to the outside, and is more or less transversely elongated and is depressed on the sides scarcely more than in the center, and because the depression of the second bone is precisely fitted to this head, the second bone of the thumb is flexed and extended more than it is bent to the sides. It could be moved as well to the side if the capitulum of the first bone were perfectly round, and if it were as compressed on the sides as it is on its anterior surface. Because of the type of joint (since the capitulum is quite depressed in its inner surface), the second bone should be capable of extreme flexion into a very sharp angle; to prevent this, two ossicles [ossa sesamoidea] (T in fig. 1, ch. 25) which are compared by the Greeks to a sesame seed stand in the way here. The head of the first bone is the reason why the second bone of the thumb can scarcely be extended beyond a straight line,

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it being so slightly depressed there, and protruding here (as also on the sides) nearly as much as in its center. Nothing more readily teaches us how ingeniously, and for what reasons, Nature fashioned these things than the functions of the thumb, which after the construction of the bones is known suggest far more things to the minds of its beholders at first glance than anyone filling many pages with wordy explanations can tell.

The system of articulation of the third bone of the thumb with the second
The second bone of the thumb [phalanx proximalis] is joined with the third [phalanx distalis] (insert G and H in fig. 2 into I and K, and M into L) differently than the first with the carpus, or the the second with the first. The lower end of the second bone is divided into two more or less round capitula separated by an elongated depression which like the capitula themselves is coated with cartilage [cart. articularis]. The upper [proximal] end [basis phalangis] of the third bone has two depressions separated by an elongated projection. These depressions receive the two capitula [caput phalangis] of the second bone, while the projection of the third bone enters the depression carved between the capitula of the second bone. In this manner the second bone enters into the third and in turn receives the third bone. Both bones are so cleverly attached [articulatio interphalangealis] by mutual entry that the third bone can only be flexed and extended but not even in the least degree moved laterally. 39 The reason why the third bone is flexed to an angle but is not extended beyond a straight line and can only be straightened from a flexed position, lies in the capitula and depressions of the joint. For the capitula, which exactly match the depressions, are moved to the inside more than the outside, and are pressed down. So obscurely are they extended to the outside and positioned there that they scarcely present the appearance of a head, and so prevent the third bone from being bent backward: as we learn is advantageous for this bone when we consider its use in flexion. At the same time we infer in what ways this joint would be weakened if it could be as easily extended and moved to the sides as it is now flexed by the great providence of Nature.

The form of the first, second, and third joints of the four fingers
It is by this very type of joint that the second and third joints 40 of the remaining fingers are attached (the figures at the front of this chapter show these in order). The first of them 41 agrees for the most part with the second joint of the thumb, as we previously stated. But it moves much more to the side, though not as markedly as it is flexed. For the heads of the metacarpal bones are much extended to the inside and are pushed down, while on the sides they do not broaden out very much, but instead are actually depressed a little there, so that flexion is easier than extension or movement to the side. By contrast, the index and little finger claim the separate distinction in the first joint that they move laterally more than the middle and ring fingers, a movement which takes place chiefly from compression in the sides of the head of the metacarpal bone. But it is not because the heads of the metacarpals are less depressed on the inside that the first joint of the four fingers does not bend in an angle as sharp as the second and third joints. Rather, certain tiny ossicles [ossa sesamoidea] (V, V in fig. 1, ch 25) which look like sesame seeds perform this function because they reinforce the joint as well as preventing it from bending more loosely than it should. The first joint of the fingers flexes and extends more than the others, because the heads of the metacarpus 42 are more depressed on the outside than the heads of the finger bones; in some people they permit the joints to be extended further, the more they are depressed on the outside. We see that certain people can bend not only the first joint of their fingers remarkably far backward, but all the others as well — particularly the third.

The flexible and elegant fingers of Giovanni Centurio
A fine specimen of this is provided by a young man of the highest prospects and keenest judgment, distinguished for his noble lineage, generous character, and singular erudition in belles lettres and a variety of disciplines: Giovanni Centurio of Genoa, 43 who bends his fingers (which are unusually well-rounded and long, perfectly suited for every art, and most elegant) so amazingly backward that he can hold water in them as easily as we do in our palm. But he displays a remarkable looseness combined with unusual strength not just in the joints of his fingers but also in all the joints of his body, particularly in the joints of his ribs to the thoracic vertebrae. 44 Such, in general, is the articulation of the fingers. It readily confirms that the bones of the fingers deservedly turn out thicker next to the joints than in their remaining length.

The small processes of the third finger bone
The third bone [phalanx distalis] protrudes also on its lower end where it is attached to no other bone, and it has a rough head equipped with two small rather hook-shaped projections; this is mainly so the tendon which flexes it (tendons of muscles C and h in the 6th table of muscles, and c, b in the 7th) 45 may be attached to the entire inner surface and powerfully inserted at its end into the tip of the bone. This tendon is easily the largest of all those that move the other bones of the fingers, and makes the most robust insertion.

The digits are justly made five in number 46
It is not at all difficult to discover why five digits were fashioned if we consider for what functions the fingers are useful. If they were fewer, they would undertake a great many actions less perfectly, while there is no reason we would require more. If fewer had been formed many actions would be lost, as we will readily appreciate if we describe each in a separate account.

The dignity of the fingers 47
If the thumb (which it was convenient to have opposed to the other four and was for this reason called a)nti/xeir 48 by the Greeks as if to say promanum, “in front of the hand”) were missing, all the others would be deprived of their power, since without its aid they can do nothing — as our very judges show, who no less often than they amputate thieves’ ears take off the thumbs

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which have been used mainly to rip the top off purses and wallets. For nearly the same reason the Athenians decreed that the thumbs of the Aeginetans, who had a powerful fleet, should be lopped off. 49 Of the remaining fingers, the index and middle finger, being located next to the thumb, are likewise next in usefulness. With these we grasp small things, and we see that the operations of every craft are accomplished mainly with them. If we do anything more violent, we employ these particularly in the task. The ring finger and little finger are of less use than the others, but a use is seen in fingers with which we grasp an object that must be embraced in a circle. If something is liquid or small, 50 it is useful to tighten the fingers closely together and bend them around it. In this operation the little finger 51 is also suitable when placed against the others like a cover. If a hard object is of such a size that the fingers need to be quite spread and parted from one another to hold it, beside the fact that we see it is best held by several fingers and the fingers meet and attach themselves to several of its parts, it also readily occurs to us how useful it is for man that the fingers can be adducted to each other and considerably abducted to the sides. The thumb surrounds such a body on the inside while the other fingers come around its outside and the whole body is contained thus in a circle. This being the case, who does not know that more than five fingers would be quite superfluous when he knows that five suffice for this task?

Why the fingers are unequal 52
Why the fingers are made unequal and the middle one excels the others in length may be gathered from the fact that it is better for the ends of the fingers to attain equality whenever we grasp a mass that is greater in circumference, and when we are trying to hold a liquid or some small object in them. For firmly grasping or holding onto larger objects, or for forcibly propelling or throwing them away, an equal grasp on all sides is most suitable. The five fingers are seen to come together on the circumference of a single circle whenever we surround a perfectly spherical body with them. Moreover, to close the hands completely when our desire is exactly to enclose a small or liquid substance, the inequality of the fingers performs a manifest function, and for this the location of the thumb is in no small way conducive.

The thumb is handsomely situated
For while the thumb is opposed to the other digits in function, it was also necessary for it to be opposed to them in location. But if it were placed quite out of opposition and took for itself the middle of the carpus, it would impede the hand in a great number of uses, particularly interfering with those which we perform with the palm of either hand separately, or with both palms at the same time. It was therefore necessary for it to be placed at the side and to be very much separated from the other fingers and linked to them. And while the transverse region of the hand extends equally to the index finger and the little finger, it was better that the thumb be placed next to the index finger, and (as has been stated above) to be loosely articulated to the lower row of carpal bones. 53 For it was fitting that the hands be turned toward each other by the index fingers but turned away at the little fingers. Indeed, in extreme flexions of the fingers the little finger leaves no place empty while the index finger leaves an area of some magnitude which can be closed or blocked by the thumb in the manner of a lid.

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]