Right auricle

The right auricle (right atrial appendage) is a muscular, ear-shaped pouch-like extension of the right atrium. It lies cranially and slightly to the right of the main body of the right atrium and extends cranioventrally and to the left to overlap the ascending aorta and the pulmonary trunk.

The interior wall of the right auricle is composed primarily of pectinate muscles (musculi pectinati), which are prominent, parallel muscular ridges lining its interior. Compared with the smooth-walled portion of the right atrium (the sinus venarum), the auricle has a distinctly rough internal appearance due to these ridges.

The auricle opens medially into the main chamber of the right atrium through a wide, non-valved orifice.

Externally, it has a thin wall and a pointed, often lobulated shape, which can vary slightly among breeds and individuals.

Cranially, the right auricle is related to the ascending aorta and pulmonary trunk. Medially, it is adjacent to the right atrium proper. Laterally, it lies close to the right lung and the pericardium. It is entirely enclosed within the fibrous pericardium.