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.