Catalogs of equestrian wear from the '30s and '40s sometimes show a style of breeches with a buttoned flap front closure rather than the usual buttoned fly.  They are termed "drop front" breeches.  I own two pairs of these, and they are among my favorites.  This first pair has a label - "Made in England" and judging by the fabric and style I would say they were made in the middle '30s, before World War II restrictions were in effect.  I am wearing my 20-inch Wesco Boss boots with them.

Here I have unbuttoned and dropped the flap so you can see how it works.  Note the additional snap fastener half way down the panel.

These drop front breeches were made in Fort Sam Houston, Texas, by a tailor working under the NRA (National Recovery Act) which some of you may remember.  The breeches were custom tailored for Lt. William B. Keese on January 16, 1934.  No wonder I feel so good when I wear them!