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

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.



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