What does "retractor" mean?

Retractor: One who, or that which, retracts. Specifically: (a) In breech-loading firearms, a device for withdrawing a cartridge shell from the barrel. (b) (Surg.) An instrument for holding apart the edges of a wound during amputation. (c) (Surg.) A bandage to protect the soft parts from injury by the saw during amputation. (d) (Anat. & Zoöl.) A muscle serving to draw in any organ or part. See Illust. under Phylactolæmata.