The exact location of the fourth intercostal sternum can be determined by the sternal angle. The sternal angle is flat against the second rib cartilage, and the fourth intercostal interval is located three ribs down from the second rib cartilage. In addition, the location of the fourth intercostal space can also be determined by the nipple, which is generally flat against the fourth rib, and the lower part of the nipple is the fourth intercostal space. Through these body surface markings, the location of the ribs and intercostals can be quickly determined, so it is important to keep in mind the anatomical location of the sternal angle and the nipple to facilitate surgical line drawing and surgical positioning.