276 JAMES W. PAPEZ 
erests. Its lower margin is attached to the atrioventricular 
ring, where it appears on the external surface and gives off some 
longitudinal bundles to the coronary sinus (fig. 4, 15). The 
septopulmonary bundles overlie and intermingle with its upper 
margin. The left septoatrial bundle (fig. 6, 74) joins the deep 
portion of its upper margin with which it appears to be continuous. 
Keith and Flack (’07) have figured this bundle on the posterior 
surface. They consider it as a portion of the annular bundles 
of the atrial canal. 
Experiments to determine primary negativity over this region 
and over the posterior and superior wall of the left atrium have 
been negative (Eyster and Meek). It is clear that there is no 
impulse forming tissue in this region. 
A NOTE ON THE NERVE SUPPLY OF THE ATRIA 
The atria are supplied by both the right and left vagosympa- 
thetic nerves. a. On the right side usually three nerves reach 
the heart. These pass down in front of the right pulmonary 
artery. The lower two unite above the right pulmonary veins 
and terminate in a gangliform enlargement in the septum on the 
left side of the orifice of the superior vena cava. From this 
terminus, branches supply the interatrial band, intercaval bundle, 
and other bundles that radiate from the septal raphe. One or 
two slender filaments pass to the left anterior crest along the 
left limb of the interatrial band. 
b. The left vagosympathetic cardiac nerves terminate simi- 
larly in the left atrium above the base of the left atrial appendage 
and the upper pulmonary vein. Filaments from this terminus 
supply the left anterior and the left posterior crests, septo- 
pulmonary, and left septoatrial bundles. A small filament may 
pass to the right in the interatrial band as far as the septum. 
Much of the literature that deals with the subject is concerned 
with experimental work. The figures of Quain, Porier and 
Sharpey, Toldt, Keith and Flack, and Spalteholtz show external 
views of the atrial musculature. 
