The cardio-inhibitory fibers in the woodchuck (Marmotta monax)

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, œsophagus, 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 œsophagus, 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 anæsthetised animal without injury, and stimulated individually.