The space anterior to the crista, including the right auricle, is sometimes referred to as the atrium proper. This terminology is based on its origin from the embryonic primitive atrium. Its walls are covered by ridges called the musculi pectinati (pectinate muscles), which fan out from the crista like the “teeth of a comb.” These ridges are also found in the right auricle, which is an ear-like, conical, muscular pouch that externally overlaps the ascending aorta.