A unilateral absence of sternocostal fibers of pectoralis major muscle with unilateral presence of sternalis muscle has been noticed in right side of an adult male cadaver during routine dissection. All slips of pectoralis major muscle as well sternalis muscle innervated by medial and lateral pectoral nerves. Absence of pectoralis major has been described extensively, both as an isolated anomaly, with varying levels of hypoplasia, and in association with congenital syndromes. But the partial hypoplasia of pectoralis muscle with compensatory presence of one of the rare muscle of anterior thoracic wall the sternalis muscle make this case as unique and rare. This finding adds to our existing knowledge for the origin of sternalis, an identity not explored fully yet. Awareness of anomalous pectoralis major musculature as well presence of sternalis muscle is important for reconstructive surgeons who perform mastectomy and for radiologists during interpretation of skiagrams.