One important variant of the panniculus carnosus remnants--a superficial muscle layer in the thoracic region typical for lower mammals, is an often found variation known by the name of sternalis muscle. It was discovered for the first time by Cabrolius in 1604 and identified precisely in 1726 by Du Puy. Even today, the variation is still an object of description and attempted to be classified and defined. We found an abnormal muscle band known as sternalis muscle (m. sternalis). The variation was accompanied by a partial bilateral agenesia of the pars sternocostalis of the pectoralis major muscle. Although m. sternalis was first described 3 centuries ago, its origin is still unclear. Some authors suggest that it originates from adjacent muscles such as the sternocleidomastoid muscle, pectoralis major muscle, rectus abdominis muscle, etc. Kadanov considers the muscle a remnant of panniculus carnosus, a muscle layer located immediately under the skin in lower mammals. Our case confirms the hypothesis of the pectoral origin of m. sternalis. It is not only a rare variation of interest to morphologists, but also a structure which is important for clinicians. The location of the muscle makes it essential for general and plastic surgeons as well as for the specialists in imaging diagnostics. In conclusion we consider that this anomaly belongs to the group of the rudimentary structures in human beings, which appear to be more variable. The suggestion of its development as a possible phylogenic regularity in the evolution makes it all the more important for the morphological science and medical practice.