Mo. Rev. Stat. § 509.230
Pleading written instrument.
509.230. Pleading written instrument. — Whenever a claim, defense, or counterclaim is founded upon a written instrument, the same may be pleaded according to legal effect, or may be recited at length in the pleading, or a copy may be attached to the pleading as an exhibit.
(L. 1943 p. 353 § 55)