Shortly after the transition started to happen between tunic shirts to full button “coat cut” shirts, the question of what to do with the tails came about. Some manufacturers, like Signal in the previous post, opted for curved front shirt tails which overlapped to avoid gapping. Others, like Olus, decided to extend the tails, and make a shirt/drawers combination. Sort of a sleeved athletic union suit with a collar. These ads date from 1914 to 1916.
Horsehide arms and trim, laskinlamb trim. Generally, they had a matching sheepskin/mouton collar, slash handwarmer pockets and a belted waist. There were, of course, drastic design differences manufacturer to manufacturer. Popular in the mid to late 1930s. They were marketed as a boys and young men’s fashion. The idea (according to original ad copy) was, with the insulation on the outside, the wearer would have a greater range of motion. I didn’t see the “grizzly” name show up when searching for original ads, but it has become the catchall term for this style.