Phylogenetic Observations on the Cardiac Nerves of Vertebrates

Abstract

The phylogeny of the cardiac nerves in vertebrates may be summarized as follows (compare Figs. 2 A, B, C).
In the primitive form of the aquatic vertebrates, such as the shark, the heart is innervated by branchial rami of the vagus only through the sinus region. The bulbus region does not receive any nerve. No sympathetic element has been observed.
When the animal acquired complete lungs, a new set of cardiac nerves appears at the porta arteriosa, where the left nerve runs in the ventral furrow between the pulmonary trunk and the systemic aorta toward the right part of the ventricle; the right nerve, in contrast, to the left part. However, at the porta venosa several nerve branches preserving the primitive pattern of the shark pass along the ductus Cuvieri and the newly developed pulmonary vein to form the plexus on the wall of the sinus and the atrium. An anastomosis of the sympathetic trunk with the vagus by means of a fine bundle was observed. This picture of cardiac innervation is assumed to be a basic pattern in the lung-breathing vertebrates.
A human case is presented in which the primitive pattern of cardiac innervation can be recognized, although it is exceedingly modified by the sympathetic component dominating the vagus.