RIGHT ATRIUM (RIGHT AURICLE) OF HEART
The right atrium forms the right anterior part of the base and is above the right ventricle. It consists of a principal cavity called the sinus venarum and a blind diverticulum called the auricle or auricular appendix. The sinus venarum is the cavity into which the veins open. The auricle curves around the anterior face of the aorta and its blind end appears in front of the origin of the pulmonary artery.
- The following features are seen in the interior of the right atrium
- Smooth glistening membrane lining the sinus venarum called the endocardium, which is continuous with that of the ventricle and the blood vessels entering it.
- The opening of the anterior vena cava at the dorso anterior part of the sinus venarum, which returns the blood from the anterior parts of the body.
- The opening of the posterior venacava returning blood from the posterior parts of the body and opening in to the sinus at the dorso-posterior part.
- A ridge called the intravenous crest projecting downwards and forwards from the dorsal wall in front of the opening of the posterior vena cava. This tends to direct the flow of blood from the anterior venacava towards the auriculo-ventricular opening.
- The coronary sinus is the opening of the great cardiac vein and vena hemiazygos into the sinus venarum below the opening of the posterior vena cava. The orifice is provided with a semilunar fold of endocardium the coronary valve.
- The fossa ovalis is an oval depression in the interatrial septum at the point of entrance of the posterior vena cava and is a remnant of the foramen ovale of the foetus.
- The interior of the auricle is not smooth but crossed by muscular ridges the musculi pectinate in various directions. The musculi pectinati terminates above on a curved crest called the crista terminalis, which indicates the junction of the primitive sinus reunions of the embryo with the atrium proper and corresponds to the sulcus terminalis externally.
- The right atrio-ventricular orifice is situated at the lower part of the floor of the sinus venarum.
- Several small orifices of small cardiac veins are concealed in the depressions.
