From 1937-1947, the obverse legend had the Latin phrase "ET IND: IMP:" meaning "and Emperor of India". This phrase was taken out from 1948-1952. As part of the government decision to modernize the reverse designs, a caribou head was chosen.
Note: 1951 Low Relief and 1952 High Relief coins do exist (from sets) but are not commonly available and are much more rare than many collectors would believe.