VINTAGE AMERICAN EAGLE BUTTON DOWN DENIM SHIRT.
I have had this since the late 1990s so sizing is a little different now than it was then. I would say this fits more like a small than a medium.  
MEASUREMENTS... FROM ARMPIT SEAM TO ARMPIT SEAM ON FRONT... 17" .
FROM TOP CENTER TO BOTTOM... 21" .
100% COTTON.
ANY MINOR IMPERFECTIONS ARE CONSISTENT WITH WASH AND LIGHT WEAR.