Left atrium

LEFT ATRIUM OF HEART

The left atrium forms the posterior part of the base of the heart. It lies behind the pulmonary artery and aorta and above the ventricle. It consists of a sinus and an auricle.

The later extends on the left side and its blind end lies behind the origin of the pulmonary artery. The sinus receives the pulmonary veins, about 4 to 7 in number in two groups.

• The following features are seen in the interior
  1. The endocardium.
  2. The openings of pulmonary veins about 4 to 7 in number into the sinus.
  3. The musculi pectinate as in the right auricle.
  4. The left atrio-ventricular orifice.