The sternalis muscle is an uncommon anatomical variant. It is located on the human anterior pectoral wall, superficial to pectoralis major. This muscle has been reported both in males and females, and in whites, blacks and Asians (Barlow, 1934; Kida & Kudoh, 1991; Shen et al. 1992; Bradley et al. 1996).

Although the importance of this muscle is still a mystery, various different interpretations have been made. Clemente (1985) considered sternalis to be a misplaced pectoralis major, although some embryologists have viewed it as part of a ventral longitudinal column muscle layer arising at the ventral tip of the hypomeres (Sadler, 1995). Sadler claimed that this muscle is represented by rectus abdominis in the abdominal region and by the infrahyoid musculature in the cervical region; in the thorax, this layer usually disappears but occasionally remains as a sternalis muscle. Kitamura et al. (1985) reported a case of congenital partial deficiency of pectoralis major accompanied by an enormous sternalis. Barlow (1934), on the other hand, claimed that sternalis represents the remains of a panniculus carnosus.