In this paper the author described the results of his observations on the presence of the musculus sternalis in upwards of six hundred bodies dissected in the anatomical rooms of the University of Edinburgh. He had found it in nineteen individuals, i.e., in about 3 per cent of the bodies examined. It occurred nearly equally in the two sexes. It bore no relation to the general muscularity of the individual. In eleven subjects the muscle was single, in eight double, making together twenty-seven specimens of the muscle. The variations which it exhibited in its attachments, size, and shape, were then described. In no case were its fibres continuous with those of the rectus abdominis, or were tendinous intersections found in it, but it mostly arose either from the flattened tendon of the external oblique muscle of the abdomen, or from the cartilages of the lower true ribs, and in many instances it was continuous at its upper end with the sternal tendon of one or both sterno-mastoids, whilst in others it was inserted into the aponeurosis covering the pectoralis major. It was always superficial to the great pectoral muscle. Of the single specimens, four occurred on the right side, two on the left; whilst in the remaining five it arose on one side of the middle line, and was inserted either altogether or in part on the opposite side. It formed an excellent illustration of the truth of the general statement, that occasional and rudimentary structures are especially liable to variations in arrangement.