The sternalis muscle is a little known muscle located at the sternum. This muscle seems to be vestigial in that it doesn’t have a known function. In originates on the superior portion of the sternum and the upper part of the pectoralis muscle. It’s insertion is the cartilage of ribs 3-7, or sometimes the sheath of the rectus abdominis, or the lower part of pectoralis major. Even though this muscle doesn’t seem to have a purpose anymore it can still harbour trigger points. These points will cause pain to be felt intensely deep in the sternum, with spillover pain radiating down the inside of the arm.