First Dorsal Interosseous
The Dorsal Interossei are bipennate muscles. Functioning as abductors, the four dorsal interosseous muscles attach to the adjacent sides of the metacarpals. The first dorsal interosseous lies between the thumb and index finger.
Precision grip for the thumb and index finger requires adduction and abduction. In the precision grip, there is pad-to-pad opposition of index pulp to thumb pulp. The metacarpophalangeal joint of the thumb is both abducted and flexed. The metacarpophalangeal joint of the index finger is flexed. It may be neutral or slightly adducted, but if powerful pad-to-pad opposition is required the abductor muscle (first dorsal interosseous) can be seen contracting in the first web. The metacarpal is flexed, abducted, an opposed at the carpometacarpal joint.