The crista terminalis represents the junction between the sinus venosus and the heart in the developing embryo. In the development of the human heart, the right horn and transverse portion of the sinus venosus ultimately become incorporated with and forms a part of the adult right atrium where it is known as the sinus venarum. The line of union between the right atrium and the right atrial appendage is present on the interior of the atrium in the form of a vertical crest, known as the crista terminalis (in older texts the crista terminalis of His). The crista terminalis is generally a smooth-surfaced, thick portion of heart muscle in a crescent shape at the opening into the right atrial appendage. On the external aspect of the right atrium, corresponding to the crista terminalis is a groove, the terminal sulcus. The crista terminalis provides the origin for the pectinate muscles.