Muscle · Chest

Sternalis

Musculus sternalis

A strap of muscle lying vertically over the front of the sternum, superficial to the sternal fibres of pectoralis major and running the wrong way across them — a variant present in some bodies and absent in others. Its attachments are as variable as its presence: usually somewhere between the upper sternum or the sternal head of sternocleidomastoid above and the costal margin, the rectus sheath or the aponeurosis of external oblique below. It may be one-sided or on both sides, and its nerve supply varies with it. No consistent action is attributed to it. It is worth a page precisely because it is a normal variant, and it is the clearest reminder in the chest wall that two bodies opened side by side do not always match.