Examine the inner surfaces of the anterior and posterior walls of the right atrium [cross-section]. The posterior wall which extends from the superior vena cava to the inferior vena cava is smooth. This area is called the sinus venarum [cross-section].
The anterior wall of the right atrium is covered with a series of parallel ridges of cardiac muscle, called pectinate muscles [probe] [cross-section ]. These muscles end on a prominent ridge called the cristae terminalis [probe] close up [cross-section ] which is located between the pectinate muscles and the sinus venarum.
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