Ultrastructural features of the myelin sheath of Scarpa's ganglion cells in the adult guinea pig

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Abstract
It is well known that the ganglia of Scarpa and Corti are formed of bipolar cells whose bodies are surrounded by a myelin sheath. Ballantyne and Engstrom have shown that 2 types of cells, 10% of them devoid of a myelin sheath, can be discerned in the guinea pig, cat, squirrel and monkey. In cells with a sheath, both in different cells and in different areas of the same cell, this is sometimes loose, while occasionally it is composed of extremely irregular layers. Perre et al. observed that Scarpa''s ganglion cells in man are surrounded by 1 or 2 turns of Schwann cell cytoplasm that do not form a myelin sheath. In a later paper Perre et al. reported that the myelin sheath of these cells in the baboon (Papio papio) consists of both a compact and a loose part. In 7/75 cells the sheath is compact and resembles that of the nerve cells, though the number of layers is very much smaller. Bretos and Richter and Spoendlin have described 2 types of cells, nearly all of them surrounded by a compact sheath, in the cat and mouse, respectively: large cells with a central nucleus and small cells with an eccentric nucleus. It was previously that ganglion cells in man are devoid of a myelin sheath. Those of the baboon are wrapped mainly in a loose sheath, whereas those the rat mostly have a compact sheath.