From the December 19 & 26, 1931, issues

SANTA CLAUS CAVALRYMEN BESTRIDE STRANGE STEEDS

Captain Jinks of the Horse Marines bestrode an unfamiliar steed; but the gentleman in the cover picture mounts one more unfamiliar still. He might qualify as a trooper in the Santa Claus Cavalry, for he is mounted on a reindeer. According to the U.S. Biological Survey, reindeer are used occasionally as saddle and pack animals in Siberia, whence the original stock of the great Alaskan herds was imported; but the animals are seldom used for these purposes on this continent.