Some of the personal comments inserted by Maimonides in his epitomes of Galen's Qātāğānas (De compositione medicamentorum per genera) and Mayāmir (De compositione medicamentorum secundum locos) are discussed. The most valuable of these comments, which have neither been edited nor studied to date, is undoubtedly a lengthy and detailed discussion of medicinal weights and measures employed in Galen and subsequent medical literature. The text of this comment, found on ff. 4b-6a (pp. 6-9) of his epitome of Galen's Qātāğānas, as extant in MS Berlin 6231, is presented along with a translation. Maimonides' discussion of these weights and measures is interesting because it is based on prominent ancient sources, above all Yuḥannā Ibn Sarābiyūn (ninth century), that date from the period when the so-called canonical units were established.