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

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.



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