NSE-IR nerve fibers were observed along the entire length of the RG, and there was no obvious gradient of innervation between the proximal and distal parts. The neurons were generally clustered in ganglia varying in size; large ganglia (up to 50 neurons) were located in the MP and small ganglia (two to four neurons) or isolated neurons were observed intermingled with the longitudinal muscular fascicles of the lips. No neurons were found in the SMP. Both in the floor and in the lips, many NOS-IR fibers were observed along the entire length of the RG, parallel to the longitudinal axis of the muscle fascicles. Only a few NOS-IR fibers were located in the external longitudinal muscle layer of the floor and in the submucosa. NOS-IR neurons were located in the MP; they were more abundant in the floor than in the lips, and we rarely observed neurons located singly or grouped into small clusters of two to three cells among the muscle fascicles of the lips. NOS-IR neurons showed great variability in both size and morphology; they exhibited an irregular outline with either short, well-stained processes or an ovoid shape. In these neurons, a long process arising from the side opposite the nucleus could sometimes be seen without showing a given polarity. The neurons were more abundant in the floor than in the lips, and their number increased proceeding distally; however, their percentages were similar in the proximal and distal parts. Almost all ganglia in the floor contained NOS-IR neurons that were often arranged around the periphery of the ganglia, and some ganglia showed only NOS-IR neurons. Approximately 80% of the NOS-IR neurons in the floor coexpressed GAL; this percentage decreased in the lips (approximately 40%). Many neurons coexpressed DBH (from 32% to 58%) but rarely (less than 0.5%) TH and SP. We never observed NOS-IR neurons expressing CGRP, CALB, IB4, and NF; however, we never found neurons stained with neurochemical markers used to identify primary sensory neurons.