Mo. Rev. Stat. § 21.370: Oaths, by whom administered.

The president of the senate and the speaker of the house of representatives may administer all oaths and affirmations to the officers of their respective houses, to swear in the members of their respective houses, after first having taken the oath of office prescribed by law themselves; and the president of the senate, speaker of the house of representatives, the chairman of the committee of the whole, or the chairman of any standing, select or special committee of either house, may administer oaths and affirmations to witnesses in any case under their examination.