A unique presentation: rectus sternalis

Rectus Sternalis is a rare flat slip of muscle present parasternally in the thoracic wall. During the regular dissection of pectoral region, three slips of Sternalis muscle were observed bilaterally in an adult male cadaver. On the right side there was a single slip (RS 1) while on the left side two slips (RS2 and RS3) were present. All three slips were present anterior to the Pectoralis Major muscle of respective side and each muscle had fleshy origin and tendinous insertions. RS1 had two heads arising from the aponeurosis of External Oblique and Rectus Abdominis. RS2 had a single origin from aponeurosis of Rectus Abdominis and RS3 took its origin from the aponeurosis of Pectoralis Major muscle. Indistinct tendinous intersections were noted in both RS1 and RS3 slips proximal to fusion of both Sternalis muscle (RS1 and RS3) with each other. Out of three slips, right Rectus Sternalis was largest with breadth 3.8cm near its origin while the second slip of Rectus Sternalis on the left was longest with length of 12.5cm. RS2 was smallest and shortest among the three slips. The RS1 even presented a flattened tendon running upwards which fused with the membranous origin of right Sternocleidomastoid muscle. The Rectus Sternalis when present arises from hypomeres as longitudinal group of muscles which usually disappears in the thoracic region. The knowledge about Sternalis muscle and its variations is important for anatomists and clinicians (radiologists and surgeons) to avoid any confusion and misdiagnosis as well as anthropologists.