Fig. 1 | Nature Communications

Fig. 1

From: Augmented manipulation ability in humans with six-fingered hands

Fig. 1

The right hand’s anatomy of subject P1. A photo of the dominant right hand of one of the six-fingered subjects (a). The joints of the wrist (radio-ulnar, radio-carpal and mid-carpal) are similar to that of a normal five-fingered hand (b). Bones are in yellow, tendons in blue, muscles: so,sf,sa: supernumerary finger opponens, flexor, abductor; to: thumb opponens; ab: abductor pollicis brevis; fb: flexor pollicis brevis. The four fingers from index to little have a similar skeleton, musculotendinous attachments and nerves as the corresponding fingers of a normal hand. The thumb resembles a normal thumb, with two phalanges. However, its carpometacarpal joint to the wrist (d) is of ball-and-socket type, with three degrees-of-freedom (dof) including torsion, while a normal thumb will have a saddle joint that does not allow torsion. The musculotendinous and neurovascular structures resemble the thumb of a normal hand (b, d). The sixth finger or supernumerary finger has three phalanges and a saddle carpometacarpal joint (e). It has two extrinsic flexor tendons and a normal extensor apparatus not dissimilar to that of a tri-phalangeal digit. Interestingly, there are muscles whose origin is the second metacarpal and whose insertion is to the proximal phalanx of the finger (b, c), similar to the muscles of a normal thumb with spherical range of motion

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