The many layers of a man's 18th Century shirt shoulder seam.
On the right, the collar is sewn to shirt. The shirt is slashed at the neckline to accommodate a triangular neck gusset. A neck gusset lining is sewn underneath, so there are actually two triangles of fabric there. On the left, a gathered sleeve. The sleeve piece, sewn to the armhole seam, strengthens this area, lines and finishes the sleeve seam. On top of all of this, centered along the shoulder, a wide strap reinforcement piece is topstiched.