274 JAMES W. PAPEZ 
The right intervenous septopulmonary bundle (/2e) arches 
over the orifice of the right upper pulmonary vein. Between the 
veins it turns downward, toward the atrial junction it spreads 
over the left leaf of the septum secundum. ‘This and the forego- 
ing bundle give rise to bundles that encircle the orifice of the 
lower right pulmonary vein. 
The right septopulmonary bundle (fig. 1, 72/) arises in the septal 
portion of the node and extends upward on the right wall of the 
upper right pulmonary vein and curves downward along its 
right wall. It gives rise to circular fiber bundles that surround 
the orifice of the upper right pulmonary vem. It may be re- 
garded as the uppermost portion of the left leaf of the septum 
secundum. With the right intervenous bundle it gives origin 
to an oblique band that extends to the right onto the posterior 
surface of the inferior vena cava bridging over the atrial junction. 
This muscular bridge (fig. 6, 72e) is not always present and may 
be fibrous. 
Keith and Flack (07) have figured these bundles. They 
consider them a part of the interatrial band. The origin of these 
bundles from the septal region behind the band, however, is 
clear (fig. 2, 12). It is also apparent that they belong to the 
same superficial stratum as the band (fig. 5, 72). 
13. The left leaf of the septum secundum 
The left leaf of the septum secundum (figs. 2 and 6) commences 
in septal raphe (fig. 2, 13) and, extending backward, forms the 
right or septal wall of the left atrium in front and below the 
orifices of the right pulmonary veins. Below the lower vein 
it turns to the left, superficially to the left leaf of the septum 
primum (fig. 2, 75) with which it intermingles and becomes 
spread over the posterior surface of the left atrium (figs. 4 and 6, 
18). 
14. The left septoatrial bundle 
The left septoatrial bundle (figs. 2 and 8, 14) is a large flat 
bundle on the inner surface of the left atrium. It rises in the 
septal raphe in front of the oval fossa and below the origin of 
