The thumb has six muscles that aid in its movement. The abductor pollicis brevis surrounds the bone, while the adductor pollicis is the muscle that connects the thumb to the forefinger and the other muscles on the back of the hand. Opponens pollicis is found opposite adductor pollicis.
Flexor pollicis brevis and flexor pollicis longus are other thumb muscles. These muscles flex the thumb's carpometacarpal and metacarpophalangeal joints. They also make up the knuckles of thumb, as well as our other digits.
There is also the extensor pollicis brevis, which extends along the top of the thumb to the metacarpophalangeal joint found at the base of the thumb, and attaches to other muscles in the middle of the forearm.
The interosseous dorsal and interosseous palmar help move the fingers. The interosseous are a collection of eight muscles that extend up from the base of each finger. They are responsible for the delicate movement of fingers for typing, writing, or manipulating objects. The lumbrical muscles, another collection of four muscles that extend from the base of the finger bones along the top of the digit, aid in flexing the fingers.
The abductor digiti minimi is attached to the fifth digit along the outside of the finger. The opponens digiti minimi is found opposite this muscle. Together with flexor digiti minimi brevis, these three muscles flex and move the fifth digit.
The final muscle, palmaris brevis, covers the base of the fifth and fourth digits. It helps with stabilizing the skin of the palm for gripping objects or making a fist.