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Occurrence and Ease of Articulation of Sign Language Handshapes: The Taiwanese
A thoroughly detailed explanation of the muscles of the hand and the movements they accomplish is far too complex to be dealt with appropriately here. Nevertheless, some understanding of the physiology of the hand and forearm is critical for us to begin to understand its relationship to sign language handshapes. Therefore, for my purposes here, I make two reasonable assumptions that serve to simplify my task. First, I assume that there exists a “canonical,” or standard hand, the structure and functions of which I outline throughout this chapter. Second, although kinesiologists are still unraveling the mysteries of how the human hand moves. My hypotheses concern the movements that particular muscles allow on the basis of the positioning of a muscle, the effects of other soft structures in the hand, and the effects of the joint structures for movement.
The question of which aspects of the physiology are in fact relevant for handshapes is a reasonable one. For example, the hand may act as a whole (i.e., all five fingers together), or some subset of fingers may group together in extension while the others remain closed to the palm. So what each individual finger can do and what the hand as a whole can do is relevant to handshapes. Therefore, my discussion centers on the bones of the hand and wrist, the joints, and the muscles and other soft structures.
The Bones of the Hand
The hand and the wrist contain twenty-seven small bones: fourteen phalanges, five metacarpals, and eight carpal (wrist) bones (see figure 11). In the following sections, I discuss the bones of the fingers, hand, and wrist in turn. I will use the terms proximal and distal to refer to relative locations on the body: proximal means closer to the trunk of the body, and distal means farther from the trunk of the body.
Each of the digits is made up of small bones called the phalanges. There are fourteen phalanges in the human hand. The four fingers have three phalanges each, known as the distal phalanx, the medial phalanx, and the proximal phalanx. The distal phalanx is located near the tip of each finger. The proximal phalanx is located near the metacarpophalangeal joint (or knuckle) of each finger. The medial phalanx is the bone between the proximal phalanx and the distal phalanx. The thumb has two phalanges: the proximal phalanx (near the knuckle) and the distal phalanx (near the tip).
The skeleton of the palm, the metacarpus, consists of five bones called metacarpals, labeled 1–5 in figure 11. Each metacarpal attaches to the proximal phalanx of each respective digit. The first metacarpal is that of the thumb, the second metacarpal is that of the index, and so on. The metacarpal heads are the distal ends of the metacarpal bones, in other words, the ends of each metacarpal bone that are closest to the proximal phalanx (Romanes 1981).
The eight bones of the wrist (the carpal bones) can be divided into two rows, a distal row (located on the hand side of the wrist) and a proximal row (located on the forearm side of the wrist). The distal row of carpal bones from right to left in figure 12 are the hamatum, capitatum, multangulum minor, and multangulum major. The proximal row of carpal bones from right to left are the pisiform, triquetrum, lunatum, and navicular. The distal ends of the two bones in the forearm, the radius and the ulna, are attached to the proximal row of carpal bones.