Doctor Otto Octavius may have been a power-mad scientist bent on world domination and the utter ruin of his nemesis, Spider-Man, but the guy had some surprisingly cogent thoughts on prosthetics development. And although mind-controlled supernumerary robotic limbs like Doc Oc's still only exist in the realm of the Marvel Universe, researchers here in reality are getting pretty darn close to creating their own. And in the near future, we'll be strapping on extra appendages whenever we need a helping hand -- or supplemental third thumb. Supernumerary Robotic Limbs (SRLs) are not prosthetics. They are designed to supplement a person's existing full complement of limbs as opposed to replacing the lost functionality of a missing one.