Three-dimensional structure of the presynaptic nerve ending in the ciliary ganglion of the chick embryo: a scanning electron microscopic study.

Presynaptic nerve endings in the ciliary ganglia of chick embryos are 3-dimensionally examined by scanning electron microscopy. Underdeveloped nerve endings attached to the lateral side of the ciliary cells are spoon-like, and show an irregular surface texture and marginal outline with many slender processes and pores. Well-developed nerve endings embracing more than half of the surface of the ciliary cell are cup-like, and show a smooth surface texture and a linear marginal outline with few slender processes and pores. The slender processes come into intimate contact with each other at the margin of the spoon-like nerve endings or cross the pores, seemingly expanding and smoothing the nerve endings. Cytoplasmic processes of the ciliary cells are also described.