During dissection of an anterior chest wall, bilateral appearance of the sternalis muscle (SM) was observed. The clavicular origin of the left sternocleidomastoid (SCM), the sternal origin of the right SCM, and both the left and right SMs together form an X-like structure. The crossing point of this structure is the tendinous band as the common origin of both SMs. Both SMs travel down inferolaterally and symmetrically to insert on ipsilateral 5th – 7th ribs and the aponeurosis of the external oblique muscle. The innervation to the muscle could be traced to the 4th, 5th, and 6th anterior intercostal nerves. Awareness of the location of the sternalis will help medical doctors avoid misdiagnosis during mammography or misjudgment during breast surgery. Because of its superior attachment to the SCM, therapists may need to be aware of that a person with such an anomaly may have an automatic accessory inspiration with head rotation.
