A supernumerary muscle mass corresponding to a right sternalis muscle was found in the anterior chest wall of a 67year-old Spanish female cadaver during a routine anatomical dissection class. The sternalis muscle is unknown for many medicine and health sciences undergraduate students because it is not included in basic texts on human anatomy. Consequently, this muscle is often unknown even in clinical practice and, in most cases, it is found in a living subject during radiological examination

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... ometimes leading to diagnostic error) or during thoracic surgery. In the latter case, it may be used for reconstruction in plastic surgery. This paper intends to bring attention to this muscle, which, despite being an infrequent anatomical variation, is not rare, and to raise awareness about its clinical importance. It is, therefore, crucial to know about its possible presence in the human body.