The ultrastructure of the geniculate ganglion.

The ultrastructure of the geniculate ganglion was studied in the guinea pig and monkey. Two cytologically distinct colonies of ganglion cells were seen and identified as light and dark cells. All neurons were unmyelinated and most were unipolar, although a few bipolar cells were seen. The axons, upon leaving the cell bodies, followed convoluted courses in the vicinity of the cells bodies before becoming invested by myelin sheaths. Two types of nerve terminal were identified on the small light cells. The first type contained predominantly agranular and spherical vesicles and had synaptic contact with the cell body. The second type did not show synaptic contacts but contained many ellipsoidal vesicles. This study provided no information on the functional significance of these nerve terminals.