Peripheral development of the avian vagus nerve with special reference to the morphological innervation of heart and lung.

The development of the cardio-pulmonary innervation was studied in whole-mount specimens of chick embryos stained with the anti-neurofilament protein (NFP) antibody. From the morphological point of view, vagal branches could be classified into two categories, i.e., the branchial branches primarily related to the pharyngeal arches, and intestinal arborization derivatives which are associated primarily with the primitive gut. The former consisted of the superior cardiac branch innervating the truncus arteriosus of the heart, and the latter, the sinal branch, pulmonary branches as well as recurrent nerve and the other intestinal branches. The superior cardiac branch at first develops as a pair of branchial branches which passes into the truncus arteriosus at stage 25, and later rotates along the aortic arch 6, thus making an asymmetrical configuration by stage 27. The sinal branch is a medial branch which first develops at stage 24. It arises from the junction of each intestinal arborization in close association with the pulmonary branch.