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 26 On the Metacarpus 1

[Comments on the Figures of Chapter 26]
The figures for this chapter are to be found in the first and second figures of the preceding chapter, representing the hand and therefore the metacarpus (marked I, II, III, IIII). The first figure of the chapter which follows will represent at the letter A the metacarpal that supports the index finger, free of other bones.

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The term “postbrachial” is preferable
The part of the hand that goes from the carpus to the root of the fingers (I, II, III, IIII in figs. 1 and 2, ch. 25, G in the skeletons) [ossa metacarpi] is what the Greeks called metaka/rpion; 2 Celsus and a large number of translators of the Greeks called it the palm. 3 Still others call it the comb, pecten, and sometimes the pectus. 4 But because the word “palm” is more widely known and most writers include the carpus in the palm, and for others “palm” means the same thing as vola, 5 and since the names pecten, pectus, and sth/qoj are also equally accepted for the metatarsus 6 of the foot, I have so far called the metaka/rpion “postbrachial.”

The metacarpus is counted as four bones by some, five by others
For Galen, the metacarpus is made up of four bones. But for Eudemus 7 and Celsus, 8 and (as can be gathered from the first book of De historia animalium 9 ) even Aristotle, there were five. These count the first bone of the thumb (A nearby 5 in figs. 1 and 2, ch. 25) [os metacarpale I] with the metacarpus because it is articulated with the fifth carpal bone [os trapezium], whereas Galen counts it with the finger bones. Many people assign it to the metacarpus because it is located in virtually the same row as the metacarpal bones and is not exposed, as are the first internodes [phalanges proximales] (D in figs. 1, 2, ch. 25) of the other fingers, but lies somewhat concealed like the metacarpals, and only two bones are commonly attributed to the thumb 10 — notwithstanding that this bone of the thumb [os metacarpale I] is both shorter than the metacarpal bones [ossa metacarpi II-V] and not as conterminous with them as they are with themselves. Moreover, they include the first bone of the thumb with the metacarpus perhaps because the second bone [phalanx proximalis] of the thumb is articulated with the first in nearly the same way (C, D in fig. 1, ch. 27) as the first bone of the fingers is articulated with the metacarpals: 11 the former [phalanges proximales] receive the round and simple heads [capita metacarpi] of the latter [ossa metacarpi] in a simple depression [basis phalangis]. Finally, they were perhaps influenced by the fact that they thought no tendon that serves to move the first thumb bone is inserted therein, just as no tendon responsible for its separate motion is inserted in any metacarpal bone. 12 A great many muscles that are inserted only in the first bone of the thumb have, in fact, escaped the notice of other anatomists. Indeed Galen (who missed at least three or four muscles of this internode (1, 2, 3 in the 7th table of muscles, and l in the 6th), 13 as you will hear in the second Book) counts the first internode of the thumb [os metacarpale I] with the fingers [ossa digitorum], to which he assigned three bones each, because it is articulated above and below by diarthrosis [articulatio synovialis], i.e., a loose type of joint and one that produces manifest movement: above it is articulated to the carpus [articulatio carpometacarpalis pollicis] 14 and below to the second bone of the thumb [articulatio metacarpophalangealis pollicis], while four metacarpal bones 15 are attached by this type of joint only below, where they are connected to the fingers. Above, according at least to Galen, they are articulated to the metacarpus [articulationes carpometacarpales] by synarthrosis, 16 a kind of joint which shows a quite obscure and scarcely perceptible motion. That is the use I believe Galen makes of the term “synarthrosis” in the nineteenth chapter of his book De Ossibus. 17 But it is by no means to be thought that Galen inspected the metacarpal bones so casually in ape or dog as to maintain that these bones are attached to the carpus by suture, in the manner of a nail, 18 or by harmonia [articulatio plana], though that would be his opinion if we stated here that he had not forgotten the view which he maintained at length when enumerating the types of synarthrosis in the beginning of his book De Ossibus. 19 Be that as it may, to adapt ourselves more correctly to the view of Galen we shall always count the metacarpals as four and the bones of the fingers as fifteen.

The character of the four metacarpal bones: length
The metacarpal bones are longer than the other bones of the fingers, and they are for the most part smoothly rounded. The longest 20 is placed before the index finger [digitus secundus] and they become gradually shorter, 21 so that easily the shortest and slenderest of them all is placed before the little finger [digitus quintus].

Epiphyses 22
They all have an epiphysis above (Q in fig. 2, ch. 25) and below (R in the same fig.; see the others in turn from there, comparing the first fig. to the second). 23 The upper [proximalis] (the place where it attaches is sometimes not visible even in children) is joined to the carpal bones, as we stated before, and these bones are somewhat wider at this point on the outside [prospectus dorsalis] than on the inside [prospectus palmaris] in order for the metacarpus together with the carpus better to form a convex surface on the outside and a hollow one inside.

Their interconnection
Indeed, these epiphyses touch each other on the sides and are attached together by a cartilaginous ligament. 24 The lower epiphyses are large as well, 25 and end in a round head [caput metacarpale] that is elongated from the outside of the hand to the inside; this is covered with cartilage and enters the concavity [basis phalangis] of the first bone of the fingers [phalanges proximales]. These epiphyses also touch each other on the sides, but not so tightly as the upper ones which are attached to the carpus; nevertheless, where they face each other they are hollowed out and put forth cartilaginous ligaments 26 by which they are strongly held together.

The spaces between the metacarpals
In the middle of their course along the length of the metacarpus, since the bones are much thinner than their epiphyses, they are separated from each other and stand apart by a noticeable interval (S in figs. 1 and 2, ch. 25). This is for an important purpose, for in any of the three intervals which the four metacarpal bones form, two muscles are located [m. interosseus palmaris et m. interosseus dorsalis] (see under D in the 8th table of muscles, and m in the 12th) 27 of the eight which flex the first bone of the four fingers. Just as two of those muscles go to each digit, so also two are extended along each metacarpal bone, and six are gathered in the three spaces, while a seventh [m. interosseus dorsalis primus] is run on the inner side of the metacarpal bone that supports the index finger, and an eighth [ m. opponens digiti minimi?] is directed along the outside of the bone that precedes the little finger. 28

Why the metacarpal bones give way to muscles
But because these muscles are scarcely longer in their course than these bones, and the intervals are not so wide that an adequate mass of muscle can be placed in them, the metacarpal bones rightly appear concave on the inside [palmaris] where they form the palm,

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1so that here also a portion of the muscles 29 may obtain a safe and fitting seat. But on the outer [dorsalis] side of the bones, the muscles do not protrude or go the least bit outside the convexity of the bones, making a surface that is level with the bones. Indeed, as we showed that the ulna and radius give way to the muscles tensioned upon them, so also we see metacarpal bones that are angular along their longitude and bulging handsomely along certain lines, without doubt on account of muscles 30 which are stretched out along them. 31 They are no less elegantly roughened on their upper [proximal] end in order to take an opportune insertion of the three muscles (one is L [m. flexor carpi radialis] in the 3rd table of muscles, another L [m. extensor carpi radialis] in the 11th, the other L [m. extensor carpi ulnaris] in the 9th) that flex 32 the carpus. This is not the only similarity of the metacarpals with the radius and ulna; they also possess a long cavity inside [cavitas medullaris] (like the one shown at D in the fig. inserted in ch.1 illustrates) suitable to contain marrow. That the metacarpus is very justly formed of four bones is clearly shown by the four fingers that are steadied by them; the fifth [pollex] needed to be opposed to them, 33 so to speak, if the hand was to be a convenient instrument for grasping. But now it would be more fitting also to devote a special chapter to the fingers.

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]