STRUCTURE OF NEKVE-CELLS. 



317 



nervous system. For example, the cells from the spinal ganglia of man and most 

 vertebrates are of a rounded shape (see fig. 366), those from the sympathetic 

 ganglia are more angular (fig. 367), those from the grey matter of the spinal cord of 

 an irregular form, and provided with numerous branching processes (fig. 368) ; 

 those from the cerebral convolutions conical, those from a particular layer of the 



Fig. 366. Two NERVE-CELLS FROM A SPINAL GANGLION (HUMAN) (Retzius). 



sh, nucleated sheath ; n, n, nuclei of the primitive sheath of the nerve. From each cell a fibre can 

 be seen to arise, and after a convoluted course on the surface of the nerve-cell, to bifurcate (opposite d) ; 

 from which point the divisions pass either in the opposite direction to one another, as in A, or at first in 

 the same direction as in B. The nuclei of the sheath, of the nerve-cell are all represented in B, but only 

 those seen in profile have been represented in A. 



Fig. 367. A GANGLION-CELL WITHIN ITS SHEATH ; FROM THE HUMAN SYMPATHETIC. 



HIGHLY MAGNIFIED. (Key and Retzius.) 



grey matter of the cerebellum, flask- or retort-shaped (fig. 374, c), and so on. Other 

 cells, situated in the course of certain nerve-fibres, are somewhat spindle-shaped, the 

 two poles of the spindle being prolonged into the nerve-fibre. 



Nerve-cells vary much in size as well as in shape. Many of the nerve-cells in 

 the body are very large, but there are others which are quite small. The latter are 

 especially abundant in the deeper part of the grey matter of the cerebellum and in 

 the retina, where they form what are known as the granule-layers (fig. 374, d). 



Structure. The nucleus of a nerve-cell is usually a large clear round vesicle 

 containing a very distinct highly refracting nucleolus, and, in some cases, an intra- 

 nuclear net-work. The cell-substance is finely granular or punctated, sometimes 

 indistinctly striated, or reticular in appearance. Cells are often to be seen which 

 contain very distinct brown or yellow coloured patches caused by an accumulation 



Y 2 



