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 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



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