1. A case of bilateral extensordigitorum brevismanuscausingsymptomsisdescribed. A review of the literature has revealed fourteen previous cases in which the anomaly was recognised.

2. The phylogenetic and morphological significance of this atavistic structure is considered.

3. Observations are made on the clinical features of the condition. It usually presents in a young male manual worker who complains of pain and swelling on the dorsum of the hand after heavy work. There is a visible swelling with the physical characteristics of a small fleshy extensor muscle.

4. Various methods of treatment are discussed. If the symptoms warrant operation total ablation of the muscle is suggested.