A prosthetic hand structure, said structure comprising: - at least one mechanical finger (110a-110e) comprising: - a metacarpal support; - a proximal stiff link connected to said metacarpal support by a proximal cylindrical joint, said proximal stiff link arranged to carry out a rotation of predetermined amplitude (φ) with respect to said metacarpal support about an axis of said proximal cylindrical joint; - a transmission member (116, 117) connected to said proximal stiff link, said transmission member (116, 117) arranged to actuate said proximal stiff link in order to cause said rotation of predetermined amplitude (φ); - an actuator arranged to operate said transmission member (116, 117); said prosthetic hand structure characterized in that said transmission member (116, 117) comprises: - a worm screw having a thread profile, said worm screw being integral to said proximal stiff link and arranged to carry out a rotation about a longitudinal axis of said worm screw; - a flexible rack having a first end portion, which is pivotally connected to said metacarpal support, and a second end portion, which is arranged to engage with said thread profile of said worm screw at an engagement zone of said flexible rack; and in that said actuator is mounted to said mechanical finger (110a-110e), said actuator arranged to actuate said worm screw, obtaining said rotation about said rotation axis, in such a way that, when said actuator moves said worm screw, a moving away/approaching movement of said engagement zone is obtained from/to said first end portion, causing said rotation of predetermined amplitude (φ), in a direction of rotation, or in the opposite direction of said proximal stiff link about said axis of said proximal cylindrical joint, said rotation of predetermined amplitude (φ) corresponding to the extension/flexion movement of the mechanical finger (110a-110e). - at least one mechanical finger (110a-110e) comprising: - a metacarpal support; - a proximal stiff link connected to said metacarpal support by a proximal cylindrical joint, said proximal stiff link arranged to carry out a rotation of predetermined amplitude (φ) with respect to said metacarpal support about an axis of said proximal cylindrical joint; - a metacarpal support; - a proximal stiff link connected to said metacarpal support by a proximal cylindrical joint, said proximal stiff link arranged to carry out a rotation of predetermined amplitude (φ) with respect to said metacarpal support about an axis of said proximal cylindrical joint; - a transmission member (116, 117) connected to said proximal stiff link, said transmission member (116, 117) arranged to actuate said proximal stiff link in order to cause said rotation of predetermined amplitude (φ); - an actuator arranged to operate said transmission member (116, 117); - a worm screw having a thread profile, said worm screw being integral to said proximal stiff link and arranged to carry out a rotation about a longitudinal axis of said worm screw; - a flexible rack having a first end portion, which is pivotally connected to said metacarpal support, and a second end portion, which is arranged to engage with said thread profile of said worm screw at an engagement zone of said flexible rack;