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In human anatomy, the thumb is the first digit on a hand. The human thumb is fully opposable to the tips of the other fingers in that it may position itself, and be folded inward, toward the rest of the hand and fingers, if so required. It rotates at the carpometacarpal joint and so can complete the sometimes quite delicate task of grasping objects by pressing them against the rest of the hand or finger(s).
Bones The thumb consists of 3 bones: Muscles Its movements are controlled by eight muscles (each with "pollicis" in the name): In the forearm The extensor pollicis longus tendon and extensor pollicis brevis tendon form what is known as the anatomical snuff box (an indentation on the lateral aspect of the thumb at its base) where one can usually palpate the radial artery. In the hand The first three of these form the thenar eminence. Grips Typical interdigital grips include the tips of thumb and second finger (forefinger/index finger) holding a pill or other small item, or thumb and sides of second and third fingers holding a pen or pencil. Origin of the thumb The evolution of the opposable or prehensile thumb is usually associated with Homo habilis, the forerunner of Homo sapiens. This, however, is the suggested result of evolution from Homo erectus (around 1 mya) via a series of intermediate anthropoid stages, and is therefore a much more complicated link. The most important factors leading to the habile hand (and its thumb) are: The opposable thumb has helped the human species develop more accurate fine motor skills. Other animals with opposable thumbs Many animals, primates and others, also have some kind of opposable thumb or toe: See also | |||||||||||||||||||||||||||
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