The hand is composed of three parts: the wrist, the palm, and the fingers. The bony structure of the wrist is formed by the carpus, that of the palm by the metacarpus (μετὰ, below; καρπὸς, the wrist); the fingers are formed by small bones called phalanges (Fig. 25, page 80).

As the carpus is almost completely hidden by soft parts, fibrous and tendinous, we shall first proceed to enumerate the bones which compose it, and show their articulations.

Notwithstanding its small compass, the carpus is made up of not less than eight bones, which are placed in two transverse rows, one superior, or brachial (next the forearm), the other inferior, or metacarpal (next the metacarpus).

The bones of the two rows are arranged as follows, enumerating them in order from without inwards—that is, from the radial to the ulnar border of the wrist:—The four bones of the first row are: the scaphoid (S, Fig. 28), named from the cavity on the inferior surface being compared to a boat (σκάφη, a boat; εἶδος, form); the semi-lunar (L, Fig. 28); the cuneiform (C, Fig. 28) (whose names indicate their shape); and the pisiform (P, Fig. 28), which, small and rounded, is placed on the anterior surface of the cuneiform bone, and articulates with it alone (Fig. 29). The four bones of the second row, still naming them from without inwards, are (Fig. 28): trapezium, trapezoid, os magnum, and unciform bones (uncus, a hook).

An examination of the bony structure of the carpus as a whole shows that the anterior or palmar surface presents the form of a vertical groove, limited on the inner side by the forward projections of the pisiform and unciform bones, and on the outer side by the projections of the scaphoid and trapezium. This groove is formed into a canal by means of a broad fibrous band (the anterior annular ligament of the wrist), which passes like a bridge across the wrist between the prominences just named. Beneath this bridge, and in the canal thus formed, pass the tendons of the flexor muscles of the fingers, the fleshy bellies of which occupy the forearm, while their tendinous insertions are attached to the phalanges. This explains the fact that these tendons, seen at the lower part of the forearm, are not visible superficially during their passage into the palm of the hand.

The Wrist-Joint.—The radio-carpal joint is formed by the convex upper surface of the carpus, constituted by the scaphoid, semi-lunar, and cuneiform bones, articulating with the lower end of the radius and the fibro-cartilage of the wrist (which lies below the ulna). This articulation permits movements of the hand in four directions: forwards and backwards (flexion and extension); outwards and inwards (abduction and adduction).

Inter-carpal Joint.—The several carpal bones glide upon one another: and there is only a limited movement possible of flexion and extension between the three named bones of the first row (scaphoid, semi-lunar, and cuneiform) and the four bones of the second row; but lateral movements are very limited and practically absent.

It is thus obvious that the movements of flexion and extension of the hand at the wrist-joint are extensive, and amount almost to a right angle, both before and behind, the mobility of the radio-carpal and inter-carpal articulations aiding each other in these movements; on the contrary, the lateral movements of the wrist are more limited, as they are confined to the radio-carpal articulation, and are restricted on the outer side (abduction) by the downward projection of the lower end of the radius. Adduction is a much more powerful movement, rendered freer by the presence of the triangular fibro-cartilage of the wrist, and the separation of the ulna and the cuneiform bones. It should also be noted that in flexion of the hand, when it forms a right angle with the forearm, the posterior surface of the wrist does not present an abrupt curve, but rather a rounded form; the convexity being made up of two series of articulations, the radio-carpal and the inter-carpal articulations.

The metacarpus (Fig. 29), or skeleton of the palm of the hand, is composed of five slender, long bones—the five metacarpal bones—separated from each other by interosseous spaces. Each metacarpal bone, like the other long bones, is composed of a shaft and two extremities. The shaft is more or less prismatic and triangular; the upper or carpal extremity is cuboid, or wedge-shaped; the lower or digital end is rounded to articulate with the first bone of the finger. The five bones are distinguished by the names, first, second, third, fourth, and fifth metacarpal, counting from the thumb to the little finger; or, again, by the name of the finger to which they correspond (as the metacarpal bone of the thumb, index finger, etc.). The first metacarpal bone, or that of the thumb, is the shortest, and is remarkable for characteristics to which reference will be made later; the second, or metacarpal bone of the index finger, and the third, or that of the middle finger, are the longest. The third is generally longer than the second, so that a line passing through the heads of the series of metacarpal bones describes a curve with its convexity downwards, of which the most prominent part corresponds to the head of the third metacarpal bone. When the hand is firmly closed, and the fingers bent in the palm, it is the head of the third metacarpal bone which forms the most prominent part of the fist.

The metacarpal bones articulate with the carpus by their upper extremities, or bases. In these articulations a very different arrangement is found for the first metacarpal bone when compared with that of the other four.

The articulation of the metacarpal bone of the thumb is formed by a saddle-shaped facet on the trapezium, concave from side to side, and convex from before backwards, and a corresponding facet at the base of the first metacarpal bone. It results, then, that as the rider can move himself on his saddle forwards and backwards, and to either side, so the metacarpal bone of the thumb is equally movable in all directions, and can accomplish the movement of circumduction, by which the extremity of the thumb describes a circle. This mobility permits the thumb to be separated from the other fingers, or to be drawn across the hand, or to touch the tips of the other fingers. This last is called the movement of opposition of the thumb, and it is owing to this property that the thumb possesses of opposing itself to the fingers that the hand of man forms such a wonderful organ for prehension and for performing the most delicate and refined movements. The articulation of the trapezium and metacarpal bone, which is the source of these movements, thus deserves particular mention. The articular surfaces of the two bones are attached to each other by an articular capsule sufficiently loose to allow all the movements of which the first metacarpal bone is capable.

On the other hand, the articulations of the metacarpal bones of the four other fingers do not present any such mobility. In fact, whilst the base of the first metacarpal bone is free, without being connected with that of the second, the bases of the other metacarpal bones are in contact with each other by their lateral surfaces, and are united by dorsal, palmar, and interosseous ligaments. Again, the transverse line of union between the second row of the carpus and the base of these metacarpal bones (carpo-metacarpal line) is irregular, the carpus and metacarpus being dovetailed into each other, especially at the level of the second and third metacarpals, by reason of the projection upwards of the second metacarpal bone, and the projection downwards of the os magnum (Fig. 29). The carpus and the four last metacarpal bones therefore form a series of joints, of which the parts are only slightly movable one on the other, giving a certain elasticity to the whole. The effects of pressure or sudden shock are avoided by the presence of numerous parts united in such a manner as to glide one on the other, at the same time not presenting any independent mobility.

The fingers are formed of a series of slender bones placed end to end, and termed phalanges. Each finger has three phalanges, except the thumb, which has only two. We distinguish the rows of phalanges by the names of the first, second, or third, counting from the base to the free extremity of the fingers; and we give the name of ungual phalanx to the last because it supports the nail. These phalanges, like the other long bones, are made up of a shaft and two extremities. The shaft is semi-cylindrical in shape, rounded behind and flattened in front, where the flexor tendons of the fingers are lodged. The extremities present characters which will be pointed out when the articulations of the fingers are studied.

The articulations of each finger are: the metacarpo-phalangeal articulation, the articulation of the first with the second, and the articulation of the second with the third phalanges (inter-phalangeal articulations).

Each metacarpo-phalangeal articulation is formed by the globular head of the metacarpal bone being received into a glenoid cavity in the base of the first phalanx. Such an adaptation of articular surfaces will permit every kind of movement, and it is easy to understand that each finger can be bent on the metacarpus, straightened, and also inclined to either side (abduction and adduction—the act of separating and bringing together the fingers); but the articular capsule or fibrous band which surrounds each metacarpo-phalangeal joint fixes an exact limit to these movements. Flexion is a much more powerful movement than extension, because the capsules of the joints are deficient behind, their places being taken by a membranous expansion of the extensor tendons which passes over the backs of the joints. Thus extension cannot usually be prolonged further than that position in which the axis of the fingers forms a straight line with that of the metacarpal bones, for just then the anterior portion of the capsule is put on the stretch, and as this part is fibrous, thick, and resisting, it prevents any increase of extension. When the anterior ligament is thinner and more relaxed, as sometimes in the female hand, the fingers can be straightened beyond the straight line, and form an obtuse angle with the metacarpus. On the other hand, this capsule is strengthened on either side by a lateral ligament, which, being inserted at the posterior part of the head of the metacarpal bone, is put on the stretch when the act of flexion is produced, and when this act of flexion arrives at a right angle, the lateral ligaments do not permit it to be carried any farther. It is easy to prove this upon ourselves, as we cannot flex the first phalanx on the metacarpus beyond this point, and we cannot, in any case, bring the anterior surface of the first phalanx of a finger in contact with the palm of the hand, but only the second and third phalanges.

Inter-phalangeal Articulations.—The articulations of the phalanges—that is, those of the first with the second, and those of the second with the third—are constructed on a different plan from the metacarpo-phalangeal articulations. Instead of a head received into a glenoid cavity, we find here, at the inferior extremity of the first and second phalanges, a surface formed like a pulley, or trochlea, with two lateral lips separated by a groove or hollow (Fig. 29); and, on the other hand, on the superior extremity of the second and third we find two cavities corresponding to the lips of the pulley, separated by a median projection which corresponds to the groove. Therefore, given a single phalanx, it will be easy to say whether it is a first, second, or third phalanx, as the first phalanx has at its upper end a single articular cavity, while the second and third have two placed side by side; and again, the third, or ungual, phalanx may be distinguished at the first glance from the second by the shape of its free extremity, which is expanded in front into a rough surface shaped like an arrow-head for the support, not of the nail, but of the pulp of the finger. The inter-phalangeal joints reproduce on a smaller scale the pulley, or trochlea, and joint of the elbow, and present an analogous mechanism permitting only the movements of flexion and extension. In fact, as each of us may prove upon his own hand, while the fingers may be moved from side to side at their metacarpo-phalangeal articulations, the several phalanges can only be flexed and extended at the inter-phalangeal joints; in other words, while the finger enjoys great freedom of movement at its base, it only possesses that of flexion and extension in its component parts. Here again, and for the same reason, flexion is the more powerful movement. The movement of extension of the phalanges is limited, because the anterior portion of the articular capsule put on the stretch by the movement is stout and strong, but we find a great variety in different subjects, and with some, such mobility that the terminal phalanges can be bent backwards. Flexion is limited only by the contact of the soft parts on the anterior surface of a phalanx.

The Proportions of the Upper Limb.—Having examined the skeleton of the upper limb in relation to form and movement, it is necessary next to study its proportions—namely, to inquire, on the one hand, what comparison the length of the limb bears to the height, and, on the other, to compare the length of the different segments of the limb with each other.

The comparison between the upper limbs and the height may be expressed in two ways: first, by examining the two arms outstretched in the horizontal position; the distance which then separates the extremity of one hand from that of the other is termed the span of the upper limbs, and this transverse measure includes not only the length of the arms, but also the breadth of the shoulders; secondly, by examining the upper limb hanging vertically beside the body, and noting to what level on the lower limb the extremity of the hand (nail of the middle finger) reaches.

The relation of the span of the upper limbs to the height has been expressed long since by the formula known as the square figure of the ancients (Fig. 30). If we draw two horizontal lines, one at the soles of the feet (c, d), the other at the summit of the head (a, b), and two vertical lines at right angles to the extremities of the two arms horizontally outstretched, these four lines form by their junction a perfect square; in other words, the man having the arms horizontal is enclosed within a square. This shows that the span of the arms is equal to the height.

This statement is correct for a man of the Caucasian race of the middle height, but it is not so for the yellow and black races, in whom the span of the arm is greater than the height. If from man we pass on to the anthropoid apes (chimpanzee, gorilla, &c.), we find that the span of the arms in these becomes more and more extended as compared with the height. Thus, in the gorilla, the height being 5 ft. 7¼ in., the span becomes 8 ft. 9¼ in.; and in the chimpanzee, to a height of 5 ft. 5¼ in. the corresponding span is 6 ft. 6 in.

Again, when we examine the upper limbs hanging freely beside the body, we find that in the European of average height the extremity of the middle finger corresponds in general to the middle of the thigh; in subjects of short stature this extremity of the hand descends a little lower than the middle, and, on the other hand, in very tall men it ends at a higher level. In the yellow and black races the extremity of the hand descends much lower than the middle of the thigh; and in the anthropoid apes we find that, in the chimpanzee, the extremity of the hand descends below the knee; in the gorilla it corresponds to the middle of the leg; and, finally, in the orang-outang, and in the gibbon, it reaches almost to the ankle.

If we seek among the various portions of the upper limb a part which would answer as a common measure between them, we cannot find anything satisfactory in this respect. The length of the hand, which would naturally seem to be indicated as a measure, is not contained an even number of times in the length of the bones of the shoulder, arm, or forearm. If, however, we take from the hand the length of the third phalanx of the middle finger, we have a measure equal to that of the vertebral border of the shoulder-blade, or of the clavicle. Under those conditions we may say that the length of the humerus is equal to twice that of the hand, and that of the forearm equal to one and a half the length of the hand; but these proportions are so variable that they cannot be insisted on. We should attach more importance to the rule that takes the hand as a common measure of the entire body in regard to height, taking the height as being equal to ten hands. This is a proportion which often answers in reality, but which presents too many exceptions to be laid down as a law.

We may here state the fact once for all, that there is not an absolute rule for the anatomist, or system of proportions applicable to every class of subject, to those of small as well as those of large stature. If, on the contrary, an ideal proportion is adopted, in which a human figure has been altered, so as to correspond to the abstract conception of beauty, we say that this question of proportion belongs no longer to the domain of anatomy or observation, but that here we rather touch æsthetic doctrines; it is for this reason that we have limited ourselves, when putting forward various ideas of proportion, to indicating, within such limits as direct observation permits, whether a part of a limb might serve as a common measure for this limb or for the total length of the body.

The Egyptian canon as demonstrated by Charles Blanc, which has a certain historical interest, is that the length of the middle finger, taken as a common measure, should be contained nineteen times in the length of the body. In fact, the “Selection of Funeral Monuments” by Lepsius (Leipzig, 1852) contains the drawing of a very curious Egyptian figure, divided by transverse lines into nineteen parts (not including the head-dress). Now as several passages in different ancient authors seem to indicate that the Egyptian sculptors have taken the finger as the unit of the system, Charles Blanc very ingeniously remarks this fact, that in the figure in question, one of the horizontal lines, the eighth beginning at the soles of the feet, passes exactly at the base of the middle finger in the right hand (closed holding a key), while the seventh touches the extremity of the middle finger of the extended left hand. It seems to him, then, very probable that the distribution of these horizontal lines indicates a system of measuring the figure, and that the space between the seventh and the eighth line measures the length of the middle finger, which thus becomes the standard of this system of proportion. According to the Egyptian rule, the length of the middle finger will be found nineteen times in that of the height (Fig. 31); it may be that this rule was adopted by the Greek artists, and Charles Blanc does not hesitate to think that Polycletus, who has composed a Treatise on Proportions, with a model in marble known by the name of Doryphorus, used no other system but the Egyptian; there has been always found in a number of antique figures this same proportion of nineteen times the middle finger to the height of the body, and in the Achilles, for example, the total height does not exceed by more than ¹⁄₂₀th of an inch the length of the middle finger multiplied by nineteen.

Brachial Index.—An interesting proportion to note is that between the arm and forearm, especially as it has been with anthropologists the subject of important researches, and will familiarise us with the term index, which we must frequently make use of, especially when comparing the transverse and antero-posterior diameters of the cranium. We give, in anthropology, the name index to the number which expresses the proportion of one dimension to some other, this last being represented by 100. Supposing, in fact, that we compare one length, A, equal to one metre, with another length, B, equal to two metres, in this case, the first length being half that of the second, we speak of the index found as 50 (because 50 is the half of 100, and we suppose the second length to be equal to 100). Now the forearm is shorter than the arm; it represents about three-fourths of it; if, then, we take the number 100 to represent the length of the humerus, the number 75, which is three-fourths of 100, would represent the length of the forearm; and then in denoting by the brachial index the proportion of the length (always shorter) of the forearm with that of the arm (always longer) we simply say that the brachial index is represented by 75.

This method of notation, which reduces any numerical proportion to the decimal system, is very valuable, as it permits us to follow without difficulty the degree in which a proportion varies according to the race or species.

Thus we come to speak of the brachial index (proportion of the forearm to the arm) as 75. We have chosen this particular number in order to make the example easy; in reality, in adult European subjects this index is only 74—that is to say, that the forearm is to the arm as 74 is to 100. If we measure the same parts in the adult negro, and reduce to the decimal proportion the numbers obtained, we find the brachial index here is 79—or that the forearm is to the arm as 79 to 100. In the negro, then, the forearm is longer compared with the arm, as 79 is a greater part of 100 than 74. Finally, if we pass on from the human species to the anthropoid apes, we see that the brachial index comes to be 80, and even 100—that is to say, that the length of the forearm becomes equal to that of the arm; and we know, therefore, that the great length of the upper limbs in the anthropoids (page 86) is principally owing to the greater length of the forearm. But the most interesting fact is that in the human race the brachial index is not the same at different ages—thus, in the European infant at birth this index is 80; before the end of the first year it is only 77, and by degrees during childhood it descends until it arrives at 74 in the adult. This clearly shows that the humerus, during the growth of the body, lengthens in proportion more than the bones of the forearm; so that they, which were at first to the humerus as 80 is to 100, come gradually to be as 77 to 100, and finally as 75 or 74 to 100. If we were to glance at comparative osteology we should see that, in such animals as the lion or the horse, the forearm becomes longer in proportion to the humerus, so as to equal, and afterwards to surpass, the length of that bone.