Hand assembly for an arm prosthetic device

A prosthetic hand assembly comprising:

• a thumb structure;
• an index finger structure;
• and
• a middle, ring, and pinky (MRP) structure including three finger structures;
• wherein the thumb structure, index finger structure, and MRP structure are driven independently from each other by separate actuators;
• and
• wherein the MRP structure is driven by the separate actuator for independently driving the MRP structure through a double differential drive that allows independent movement of under-actuated finger structures of the MRP structure when movement of another of the three finger structures of the MRP structure is prevented.