This shirt is amazing - it's by the brand Botany, the tag says Ivy Flannel, 100% wool and I'm dating this to the 1950s based on what I've read. What's amazing about it is the number of repairs to this shirt. It was clearly loved and worn heavily for many years and lovingly mended by a skilled seamstress. See photos of the seamstresses' patch work - the repairs are really what makes this shirt special. I wonder who they were and what kind of work the owner of this shirt did.

The size on the tag says "M" and 15 to 15.5
The shoulder to sleeve measurement is 22 inches
The lay flat pit to pit measures 24 inches

This item is sold from a vintage boutique in Bloomington, Illinois.