Charles Bell's drawing of a trephination which he performed in order to remove splinters of bone from an injured skull. The shard of removed bone is shown on the sheet of paper at right. Observations of the effects of brain injuries on the movements and sensations of the body helped Bell to formulate his ideas about brain localisation. He showed that there were 2 kinds of nerve, sensory and motor, and demonstrated their points of origin in the brain. He also demonstrated that lesions of the 7th cranial nerve produced a facial paralysis which later became known as Bell's palsy.Source: Sir Charles Bell. Illustrations of the great operations of surgery. Longmans, London 1820.