The noble walrus, the lordly musk-ox, and the herculean grizzly bear continue the series of large mammals appearing on the Canadian medium-value definitive stamps. Two of these stamps - the walrus and the grizzly bear - will ben available in five-stamp packs. The musk-ox probably emigrated from Asia across the Bering Strait, when it was a land bridge, some 10,000 years ago. The animal has adapted to the harsh life on the tundra, developing a shaggy coat that is so effective an insulator that snow will not melt on it. Wolves and men are the musk-ox's only predators. When attacked, this relic of the Ice Age forms a defensive circle of animals standing rump-to-rump; while this is an effective tactic against wolves, it provides no protection from man's guns. Brian Tsang, a Toronto graphic artist, designed these three mammal stamps to suggest the animals' environment in the same graphic style used for previous stamps in the series featuring large Canadian mammals.