Part of the hand and thumb

For example, a spring-based finger and thumb mechanism is adopted in the Iowa hand Yang et al. The fourteen phalanges make up the fingers and thumb, and are numbered I-V thumb to little finger when the hand is viewed from an anatomical position palm up. Yet there is no common agreement on how the mechanism works in detail Emerson et al. As a result, these primates are unable to perform the pad-to-pad grip associated with opposability. Assumptions in kinematic hand modeling including the thumb are discussed in Bullock et al. Coordination of thumb joints during opposition. For an overview, see Anatomical terminology.

It passes through the carpal tunnel in a separate tendon sheath , after which it lies between the heads of the flexor pollicis brevis. The flexor pollicis brevis FPB has two heads. Opposability of the thumb should not be confused with a precision grip as some animals possess semi-opposable thumbs yet are known to have extensive precision grips Tufted Capuchins for example.