Any of the five digits. Any of the four terminal members of the hand, specifically those other than the thumb. A movement by which the pulp surface of the thumb is placed squarely in four paws five directions pdf with – or diametrically opposite to – the terminal pads of one or all of the remaining digits. Arguably, this definition was chosen to underline what is unique to the human thumb.
Anatomists and other researchers focused exclusively on human anatomy, on the other hand, tend to elaborate this definition in various ways and, consequently, there are hundreds of definitions. Because this stability is actively maintained by muscles rather than by articular constraints, most muscles attached to the thumb tend to be active during most thumb motions. The muscles acting on the thumb can be divided into two groups: The extrinsic hand muscles, with their muscle bellies located in the forearm, and the intrinsic hand muscles, with their muscles bellies located in the hand proper. It finally attaches onto the base of the distal phalanx of the thumb.
A part of the tendon reaches the trapezium, while another fuses with the tendons of the extensor pollicis brevis and the abductor pollicis brevis. Except for abducting the hand, it flexes the hand towards the palm and abducts it radially. Passing through the third tendon compartment, it is inserted onto the base of the distal phalanx of the thumb. Passing through the first tendon compartment together with the abductor pollicis longus, it is attached to the base of the proximal phalanx of the thumb. It extends the thumb and, because of its close relationship to the long abductor, also abducts the thumb.
It inserts to the radial sesamoid bone and the proximal phalanx of the thumb. The muscle is inserted onto the radial sesamoid bone of the metacarpophalangeal joint. It acts to flex, adduct, and abduct the thumb, and is therefore also able to oppose the thumb. It is inserted onto the radial side of the first metacarpal. It opposes the thumb and assists in adduction.