260 JAMES W. PAPEZ 
the sino-auricular node is abolished is the seat of impulse forma- 
tion for the atria transferred to the atrioventricular node. 
‘ By the methods employed I have not been able to determine 
what connections exist between the septal raphe and the sino- 
auricular and atrioventricular nodes. It is conceivable that 
remnants of sino-auricular tissue exist in the raphe or that the 
bundles that arise from the raphe are directly connected with 
both of the nodes by means of similar tissue. It is clear that 
the septal raphe contains fibrous tissue which serves as a point 
of attachment for the muscle bundles that arise in the septum. 
The question is raised whether or not the pacemaking function 
for the bundles of the left atrium and the deep bundles of the 
right atrium exists in the septal raphe. If not, what is* the 
relation of these bundles to the head of the sino-auricular node 
or. how is the excitation process conducted to them? If this 
function does exist in the septal raphe, what is the relation of 
the raphe to the atrioventricular node of Tawara? 
MUSCULATURE OF THE RIGHT ATRIUM 
1. The interatrial band 
The interatrial (interauricular) band, as shown in figure 5, 7, 
is a strong external muscular bundle on the anterior surface of 
the atria. It extends from the sino-auricular region to the left 
appendage. It is represented in Toldt’s Atlas, figure 958. Keith 
and Flack (07) designated it a ‘‘constant band passing from the 
sinus musculature to the vestibule of the left auricle.” T. Lewis 
(14) and others have adopted this name for it. Lewis found, 
in tracing the excitatation from the sino-auricular node, that the 
rate of propagation was greater along the band than elsewhere 
in the atrium. G. Bachmann (16) showed that, although, 
perhaps not the only, it is the primary or more direct path for 
the conduction of the excitatory process from the right to the 
left auricle. . 
This band (fig. 5, 7) lies on the external and anterior surface 
of ‘the atria in front of the left septopulmonary bundle (12), which 
forms the deeper and more extensive stratum in this region. 
