For my "Originals" documentation I used:
The American Frontier, by Davis, page 202, Cowboy standing on right (date ?)
&
Time-Life Old West Series, The Scouts, page 156, Al Sieber (1880s)
Plus:
Painting titled "Long Jakes" by Charles Deas done in 1844. (A copy of this painting apears on the cover of the Time-Life Old West Series, The Trail Blazers.)
They are also metioned in the 1880s Cowboy Sketchbook by Riesen (?)
Books