Frequency of Occurrence and Ease of Articulation of Sign Language Handshapes: The Taiwanese Example

Chapter Two. The Anatomy and Physiology of the Human Hand

Chapter Two The Anatomy and Physiology of the Human Hand First developing an understanding of the anatomy and physiology of the human hand and the relevance of each to handshapes will enable the reader to follow the theory I propose with respect to ease of articulation for handshapes. Although I adhere to the standard distinction between anatomy (i.e., the description of parts of the body and their potential for movement) and physiology (the study of how the parts move and interact) (Galley and Forster 1987), my discussion of the two areas will be intertwined. The anatomy and physiology of the human hand are tremendously complicated; therefore, making hard and fast conclusions about all aspects of physiology is unwise (and maybe even impossible). Enormous fields of study such as anatomy, physiology, and biomechanics are engaged in the task of understanding how the human body works (Wells 1966). Discoveries made in these areas alter previous paradigms, and consequently, aspects of both anatomy and physiology are still not well understood. For example, variation exists across humans with respect to the number and arrangement of extensor tendons (Schenck 1964). Beyond anatomy, the precise functions of anatomical structures are not necessarily clear. For example, questions still arise as to which smaller movements combine to form a larger movement and which muscles participate (and how much) in execnting particular movements (Wells 1966)-qnestions that are patticulaTly impOltant here. Different muscle groups might work together to achieve a given movement, The Anatomy and Physiology of the HUlTlan Hand 57 though one muscle might be primarily responsible. But in another movement , the same muscles might participate in different ways. So, a given muscle might act as a prime mover (i.e., actually doing some action) in one movement, as an antagonist (i.e., permitting the action by relaxing ) in another, and as a synergist (i.e., helping the prime mover to complete the action) in a third. To complicate matters, in accomplishing an action, a prime mover or a synergist may participate minimally (say, only 10-20 percent) or maximally (say, 80-100 percent). [3 Clearly then, it is impossible to say that a given muscle is a prime mover, an antagonist , or a synergist because it may function as a prime mover for one movement, as an antagonist for another, and as a synergist for a third. 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 bandshapes. Therefore, for my purposes here, I make two reasonable assumptions that serve to simplify my task. First, I assume that th~re 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 llUman 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 13. Because, anatomically and physiologicaUy, the thumb both resembles and differs from the other four fingers, the need sometimes arises to distinguish the thumb from the rest of the fingers. Throughout the chapter, my use of the phrase the five digits should be intelpreted as including the thumb and four fingers. The phrase the fingers should be intetpreted as excluding the thumb. 58 Chapter Two 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...