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Background and Objective: The sternalis muscle is a small supernumerary muscle of the pectoral region. It may make misdiagnosis as a breast mass or tumor in the mammograph. Previous studies reported different types of sternalis muscles. There has not been reported of the sternalis muscle in Northeastern Thais.
Methods: This is a descriptive study based on anatomical dissection in embalmed cadavers using in gross anatomy subject at Gross Anatomy Laboratory Dissecting room of the Department of Anatomy, Faculty of Medicine, Khon Kaen University. One hundred seventeen donated, embalmed Northeastern Thai cadavers (70 males; 47 females) ranging between 19-97 years of age at decease were used. The pectoral region of each cadaver was carefully dissected and examined for the sternalis muscle. The shape, location, nerve, and arterial supply were investigated and recorded.
Results: Sternalis muscles presented in 10 cases (8.5%) of 117 cadavers (9 males and 1 female). The right unilateral sternalis was observed in 9 specimens. Bilateral sternalis was detected in only 1 male cadaver. Each muscle was strap-like and located either parallel or upward medially to the sternum. All muscles were supplied by the 2nd - 4th intercostal nerve.
Conclusions: The incidence of sternalis muscle in Northeastern Thais was 8.5 %. Most of these (90%) were right unilateral sternalis and were found more often in male than in female.
Key Words: Anatomical variant, Northeastern Thais, sternalis muscle, sternum