No other pleading or written allegation is allowed than the writ and answer; these are the pleadings in the case, and have the same effect, and are to be construed and may be amended in the same manner, as pleadings in a civil action; and the issues thereby joined must be tried, and the further proceedings thereon had, in the same manner as in a civil action. R.L. 1910, § 4915.
Oklahoma Legal Code