From Susquehanna's 2007 yearbook.  See How to Hoodoo Hack a Yearbook.

You know the comedy-tragedy masks, with the muse of tragedy, Melpomene, and the muse of comedy, Thalia.  The lesser seen third mask is what Walter Harte called "the slatten-muse, Indifference" (Eulogius or, the Charitable Mason, 1767).  (We assume that slatten derives from the stone slab of masonry called a slatt, so as to imply stony-faced apathy.) 

Our illustration is from Emerson's 1922 yearbook.

From El Globo, 1844.  Courtesy of La Biblioteca Universitaria de Sevilla.

From Shut, 1907.

Memories of college.  From Elmhurst's 1973 yearbook.  See How to Hoodoo Hack a Yearbook.

From Purdue's 1915 yearbook.

We've never heard a good explanation, but it's true that if comedy and tragedy masks are after you, a ukulele is the best defense.  From Kansas State's 1928 yearbook.

Throwing confetti and donning masks for dogs.  From Le Journal Amusant, 1914.

Memories of college.  From Rockford's 1963 yearbook.

Memories of college.  From Olivet Nazarene's 1975 yearbook.

Here's a precursor to Daft Punk, Deadmau5, and the many DJs who wear masks in concert.  "The masked marvels of the keyboard," from Anderson's 1948 yearbook.

From L'Assiette au Beurre, 1908.

Reblog if this might be a better way to view art.  From Le Pêle-Mêle, 1896.