Investigation concerning the architecture of the atrial musculature .clates back to Keith in 1903. Descriptions of the atrial musculature of some mammals were given bY Tandler (1913), Paper (19?0), Robb (1934) and Thomas (1959). Nathan
and Eiiakim (1966) described the general directions of the flbres in the posterior wall of the human left atrium. Literature concerning the orientation and attachments of the individual muscular bundles of the human left atrium, however, is
relatively deficient.