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Surgery of the elbow joints is not uncommon to which several approaches could be made, lateral approach, posterior approach, postero-lateral approach, and medial approach (Anson and McVay, 1971). The detail anatomy of the region is as ever important as the awareness of any of deformity or variation therein. Our experience in Khon Kaen University Medical School dissecting room for 18 years with 288 cadavers supplied us one case of variation in the antecubital fossa. The presence of this superfluous muscle is assessed to interfere with the medial approach of the elbow joint surgery. It was the separate muscle covered with its own fascia and originated from the medial intermuscular septum of the brachium; ran vertically and superficial to the brachial artery and median nerve but deep to the bicipital aponeurosis; and finally joined the pronator teres tendon of insertion. The muscle received branches from the median nerve. We proposed the name “Brachio-pronatus” for this muscle. The name, “Brachial head” of the pronator teres muscle was also suggested by the Society of Anatomy of Thailand member in the 15th Annual Meeting on 22-24 April 1992. Its gross anatomy will be described and we proposed four possibities of its developmental anomaly. Its kinesiological advantage is also discussed.