Cochlear and lagenar ganglia of the chicken.

Cochlear and lagenar components of the statoacoustical ganglion in the inner ear of one chicken were studied quantitatively in the TEM. Both myelinated and unmyelinated nerve fibers were present in these two parts of the ganglion and in a putative efferent bundle within the ganglion. The cochlear portion had the lowest, the efferent bundle the highest percentage of unmyelinated fibers. Compared to the other parts of the ganglia, the cochlear fibers had a high degree of homogeneity, especially in fiber size. Some gradients in the baso-apical direction were found, such as an increase in the size of myelinated cochlear fibers from the base to the apex. Based on the ultrastructure of cellular components, no distinct populations of cell bodies within the statoacoustical ganglion were definable. The ganglion contained some 8,000 cochlear and about 1,200-2,000 lagenar neurons. The putative efferent bundle had only 150-200 fibers. This cannot be the total number of efferents to the hair cells in both the basilar papilla and the lagenar. A large number of efferent fibers to the auditory papillae presumably run mingled among the afferent fibers.