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The left atrium

The left atrium , atrium sinistrum, like the right one, has an irregularly cuboidal shape, the thickness of its wall reaches 2 to 3 mm. It distinguishes the upper, front, back and outer (left) walls. The inner (right) wall is the interatrial septum. The bottom wall is the base of the left ventricle.

Анатомия человека в картинках

From the anteroposterior wall of the auricle left the left ear, auricula sinistra. It bends anteriorly, embracing the beginning of the pulmonary trunk.

In the posterior part of the upper wall of the atrium, four openings of pulmonary veins, ostia venarum pulmonalium, through which arterial blood from the lungs enter the cavity of the left atrium, are opened. The mouths of both right and left pulmonary veins lie close to each other, whereas between the mouths of the right and left veins there is a space corresponding to the upper-posterior section of the left atrial wall.

The left atrial-ventricular opening, ostium atrioventriculare sinistrum, through which the left atrial cavity communicates with the cavity of the left ventricle is located on the lower wall of the left atrium.

Анатомия человека в картинках

The inner surface of the left atrium is smooth, with the exception of the inner (right) wall and abalone. The inner (right) wall of the left atrium has a flat depression corresponding to the oval fossa; It is bordered by a fold - a flap of the oval hole (sickle of the septum), valvula foraminis ovalis (falx septi), representing the remainder of the oval hole that existed in the embryonic period.
The inner surface of the left ear has weakly expressed comb muscles, mm. Pectinati, intertwining among themselves in various directions.
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