The supraclavicularis proprius muscle is an abnormal muscle that may be found in the supraclavicularisfossa. During routine dissection of 78 cadavers (corresponding to 156 supraclavicular fossae), 10% formalin fixed, we found it in one adult Caucasian male cadaver. In our experience, the frequency of occurrence of the supraclavicularis proprius muscle would be 0.64%. This abnormal muscle consists of an anterior tendon inserting…