The Body in Motion: Its Evolution and Design by Theodore Dimon Jr. Ed.d. & G. David Brown

Author:Theodore Dimon Jr. Ed.d. & G. David Brown [Ed.d., Theodore Dimon Jr. & Brown, G. David]
Language: eng
Format: epub
Tags: Health; Fitness & Dieting, Alternative Medicine, Reference, Medical Books, Basic Sciences, Anatomy, Reference & Test Preparation, Alternative Therapies, Personal Health, Healthy Living, Medical eBooks, Basic Science
ISBN: 9781583946916
Amazon: B009MYB950
Publisher: North Atlantic Books
Published: 2012-11-12T22:00:00+00:00

Figure 6-8. Distal joints of the thumb. (Illustration 6-8)

The most important movement of the thumb, however, takes place at a crucial but less obvious joint located right at the wrist. If you try to oppose the thumb to the fingers simply by moving at the two joints we’ve looked at so far, you’ll find that it can’t be done. It must be possible to move the entire pad of the thumb so that the thumb as a whole can be moved closer to the palm. The only way this can happen is if the thumb moves at the wrist, so that the entire pad of the thumb can be moved in relation to the rest of the hand, bringing the thumb into opposition with the fingers (Fig. 6-9).

This joint at the base of the thumb is the crucial articulation that makes opposition or prehension possible. Because the metacarpal bones are tied together, the fingers begin at the knuckles (Fig. 6-10). In contrast, however, the thumb is formed by a column of bones that begins at the wrist. And because the thumb must move freely in relation to the hand, the pivotal joint in this column of bones is the one formed at its base by the articulation of the wrist and metacarpal bones—the trapezo-metacarpal or TM joint (Fig. 6-10)—which makes it possible to freely move the pad of the thumb to oppose the thumb and fingers (Fig. 6-9b).

The use of the thumb and hand accounts for much of the complexity of the brain and many of the qualities we associate with being human. One of the great advantages of a fully upright posture is that it frees up the hands for manipulative purposes, which in turn leads to an increased ability to perceive the world three-dimensionally, to build and invent things, to explore the world with our tactile sense, to express ourselves through touch, and to correlate what we see with what we can feel and explore in our environment. This refined use of the hands is largely under our conscious control, so that it becomes a tangible expression of our creative minds.

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