Where does Holmes believe Dr Mortimer received his cane?

From the text:

If he was in the hospital and yet not on the staff he could only have been a house-surgeon or a house-physician—little more than a senior student. And he left five years ago—the date is on the stick.

“Mortimer, James, M.R.C.S., 1882, Grimpen, Dartmoor, Devon. Housesurgeon, from 1882 to 1884, at Charing Cross Hospital. Winner of the Jackson prize for Comparative Pathology, with essay entitled ‘Is Disease a Reversion?’ Corresponding member of the Swedish Pathological Society. Author of ‘Some Freaks of Atavism’ (Lancet 1882). ‘Do We Progress?’ (Journal of Psychology, March, 1883). Medical Officer for the parishes of Grimpen, Thorsley, and High Barrow.”