As I remember it, there was a piece of cloth, like muslin fabric, stitched into the crotch seam on the inside. I always thought it was weird. Was it a barrier of some kind? Like to prevent crotch sweat stains on the seat of our saddles?
Or maybe it held the crotch seams together, due to the limited stretch of that infernal fabric.
As you can see, this has troubled me for some time.