Thumb

The thumb is the short, opposable first digit of the human hand. Its position and movement let the hand grasp objects and manipulate them precisely.

Opposition (hand): Opposition is the movement that brings the thumb across the palm toward another fingertip. This distinctive motion lets the thumb meet the fingers for pinching and grasping.
Phalanx: A phalanx is one of the small bones that form the digits of a hand or foot. The thumb has two phalanges, one fewer than each of the other fingers.
Precision grip: A precision grip holds or manipulates an object between the thumb and one or more fingertips. The thumb’s opposition makes delicate fingertip control possible.
Non-opposable thumb: A non-opposable thumb cannot readily move across the palm to touch the fingertips. Its limited movement contrasts with the human thumb’s broad opposition.
Carpometacarpal joint of the thumb: The carpometacarpal joint of the thumb connects its metacarpal bone to the wrist’s trapezium. Its saddle-shaped surfaces allow the thumb to move across the palm.
Metacarpal bone: A metacarpal bone links a finger or thumb to the wrist bones. The thumb’s metacarpal rotates and moves at its unusually mobile base joint.
Power grip: A power grip holds an object firmly against the palm with the fingers and thumb. The thumb braces objects against the curled fingers during forceful grasping.
Hallux: The hallux is the innermost digit of the foot, commonly called the big toe. It is the foot’s first digit, but in humans it is not opposable.
Thenar muscles: The thenar muscles form the fleshy mound at the base of the thumb and move it. These muscles drive much of the thumb’s opposition, flexion, and abduction.
Trapezium (bone): The trapezium is a wrist bone that articulates with the base of the thumb’s metacarpal. Its joint with the thumb’s metacarpal enables a broad range of motion.

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