A cell sheath enveloping the body of the neurons in sensory ganglia was mentioned for the first time in 1836 by Valentin, a pupil of Purkinje. In some illustrations of his paper, the nuclei of cells adjacent to the surface of the nerve cell body, both in the trigeminal ganglion and in the ganglia of the autonomic nervous system, were clearly shown (Fig. 1.1a) even though they were misinterpreted as pigment granules. Since Remak (1838) denied the existence of this perineuronal sheath, Valentin (1839) provided a more detailed description of it, illustrated with new drawings (Fig. 1.1b), the captions of which gave a correct interpretation of the satellite cell nuclei.