Cardio-inhibitory Fibers in the Woodchuck. 
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The cardio-inhibitory fibers in the woodchuck (Marmotta 
monax). 
By SUTHERLAND SIMPSON and H. W. MAYES. 
[From the Department of Physiology and Biochemistry, Medical 
College, Cornell University, Ithaca, N. Y.] 
In mammals the trunk of the vagus in the cervical part of 
its course, where it is most conveniently exposed and stimulated, 
is composed of afferent and efferent fibers intimately intermixed. 
Afferent fibers come from the pharynx, oesophagus, stomach and 
other abdominal viscera, larynx, trachea, bronchi and pulmonary 
tissue, and heart; and efferent fibers pass to the voluntary muscles 
of the soft palate, pharynx, larynx, to the non-striped muscle of 
the oesophagus, stomach and intestine, and of the trachea, bronchi 
and their divisions in the lungs, and to the heart. 
In studying the functions of the afferent and efferent cardiac 
fibers by division and excitation, these cannot be separated from 
each other, nor from the afferent and efferent fibers belonging 
to other organs, except in the case of the rabbit where the depressor 
nerve containing the afferent cardiac fibers exists as a separate 
branch which can be isolated and stimulated alone. 
In the woodchuck or American marmot (Marmotta monax) 
we find that the cervical part of the vagus consists of two or three 
distinct fasciculi which can be readily isolated in the living an- 
aesthetised animal without injury, and stimulated individually. 
On ligaturing and dividing each of these strands, and stimulating 
the peripheral and central ends, we find that one of them alone 
contains cardio-inhibitory fibers. Upwards this can be followed 
as a distinct fasciculus to the superficial origin of the vagus nerve 
from the medulla oblongata, but in the lower part of the neck it 
appears to unite with the other bundles to form a common trunk 
and cannot be easily dissociated. Whether it contains afferent 
fibers, or efferent fibers to other organs than the heart, at the 
present moment we are not prepared to say, but if on further 
investigation we find that it consists of cardio-inhibitory fibers 
alone, then by tearing out the fasciculus at its point of exit from 
