The ciliary ganglion of the monkey: a light and electron microscope study

The results of light and electron microscope studies of the ciliary ganglion of 5 monkeys (Macaca fascicularis) are described. The ganglion, measuring about 2 mm in length, was consistently observed to be attached to the nerve supplying the inferior oblique muscle at its origin from the oculomotor nerve. A very fine branch was found to connect the nasociliary nerve to the ganglion. The number of neurons varied from 2824 to 3545 after applying Abercrombie's (1946) correction. The mean of the maximum diameter was 43.1 microns (S.D. = 8.0), that of the minimum diameter was 30.5 microns (S.D. = 5.4); the mean of the average diameters was 36.8 microns (S.D. = 5.5) and that of the soma ratios of the maximum to minimum diameters was 1.4 (S.D. = 0.3). The frequency distributions of the maximum diameter, the minimum diameter, the average diameter and the soma ratio were all unimodal. On light microscopy, the Nissl granules in the neurons were prominent and randomly distributed in the cytoplasm. Under the electron microscope, the rough endoplasmic reticulum was distributed either peripherally, perinuclearly or randomly in the cytoplasm of the neuron. Most of the dendrites were short protrusions from the cell body; occasionally such dendritic protrusions were electron dense. Most of the synapses encountered were axodendritic; a few were axosomatic. Synaptic complexes were frequently observed. The axon terminals usually contained a mixture of both round, measuring 30-50 nm in diameter, and flattened vesicles. Tilt analyses showed that the flattened vesicles which measured 20 nm by 50 nm were either discoid or cylindrical in shape. Large dense-cored vesicles measuring 80-100 nm, with core diameters of between 40 and 60 nm, were frequently present.