TWENTY-FIRST LECTURE. 



THE CENTRAL ORGANS OF THE NERVOUS SYSTEM. 

 GANGLIA AND THE SPINAL CORD. 



-THE 



WHEREVER the ganglion cells accumulate, the formation of 

 a central nerve organ commences. Therefore, from these 

 smallest cells, only to be discovered by means of the micro- 

 scope, up to the brain and spinal cord, with their immense, 

 frequently combined, gray substances, proceeds a continuous 

 series of developments. Our knowledge concerning the latter 

 is at present, however, very insufficient ; methods for manag- 

 ing such complicated structures are wanting. 



Let us discuss, first, the peripheral ganglia or nerve nodules 

 (Fig. 185). A connective-tissue envelope, a modified peri- 

 neurium, surrounds the organ. It sends into the interior, 

 fenestrated, leaf-like processes, the bearers of a tolerably de- 

 veloped capillary net-work. 

 The irregular and also con- 

 nected cavities are filled with 

 ganglion cells (d, e,f), placed 

 close to each other, and in- 

 vested by connective tissue. 



Between them run isolated 

 nerve fibres or bundles of the 

 same. At an earlier period 

 it was believed that both these 

 elements, the cellular and the 

 fibrous, merely lay alongside 

 of each other. At that time 

 they distinguished penetrat- 

 ing primitive fibres, which 

 passed for the most part in 

 bundles and straight through 

 the nodules, and circumgyrating, which passed singly, with 



Fig. 185. — A sympathetic ganglion of the 

 mammalial animal (diagramatic) ; a, S, c, the 

 nerve trunks ; d, multipolar cells ; d*, one 

 with a dividing nerve fibre ; e, unipolar ; /, 

 apolar. 



