THE NERVOUS SYSTEM 



433 



tinct nucleolus, and is surrounded by a capsule of flat, concentrically 

 arranged cells which are probably derived from the neural plate 

 (p. 425) and are often caWed am pJdcytes or satellite cells (Fig. 301). 

 Stained by Nissl's method the cytoplasm is seen to contain rather 

 small, finely granular chromophilic bodies, which show a tendency 

 to concentric arrangement around the nucleus. Pigmentation is 

 common, the granules usually forming a group in the vicinity of the 

 point of origin of the main process of the cell. The majority of the 



Fig. 299. — Longitudinal Section through a Spinal Ganglion. X20. (Stohr.) a, 

 Ventral ner\-e root; b, dorsal nerve root; c, mixed spinal nerve; d, groups of ganglion 

 cells; e, nerve fibres;/, perineurium; g, fat; h, blood-vessel. 



cells of the spinal ganglia have one principal process which, at some 

 distance from the cell body, divides into a peripheral branch which 

 becomes an afferent fibre of the peripheral nerv^e and a central 

 branch which enters the cord as a dorsal root fibre (p. 426). These 

 cells are usually called unipolar cells. The principal process 

 usually becomes medullated soon after emerging from the cell cap- 

 sule (Fig. 300). 



Among these cells a number of forms have been distinguished by Dogiel: 

 (a) Cells with only a principal process. This process may pass almost directly 

 from the capsule, but often takes several turns around the cell body, forming a 

 "glomerulus," before emerging from the capsule (Fig. 300, i and Fig. 301, A). 

 This form is usually represented as the typical cerebro-spinal ganglion cell, but 

 constitutes only a minority of these cells, (b) The principal process gives off 

 collaterals. These lie within the capsule or are given ofif outside the capsule and 



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