200 NINETEENTH LECTURE.  



On teasing out the spinal ganglion of a fish (the ray is most 

 to be recommended) we recognize (Fig. 175) that each nerve 

 fibre penetrates a ganglion cell, to again pass out at the other 

 pole (a, b). Broad fibres connect with larger cells, narrow 

 nerve tubes with smaller ones. 



The latter nerve fibres are probably sensory constituents 

 of the sympathetic. Numerous individual, otherwise consti- 

 tuted combinations occur, in addition to these, perhaps as 

 anomalous products of development {d, e). 



Both varieties of ganglion cells show distinctly that their 

 envelope passes over into the primitive sheath of the nerve 

 fibre connected with them. 



As a third form, we have to mention the multipolar gan- 

 glion cells. They were seen for the first time in the year 1838 

 (Purkinje). They are met with in man in the sympathetic 

 ganglia, in the retina of the eye, and in the gray substance 

 of the brain and spinal cord. 



In the so-called anterior cornu of the latter is found the 

 elegant form of our Fig. 176. 



A membraneless cell body sends off a varying, often quite 

 considerable number of delicate granular processes (b), which 

 undergo repeated divisions and continual ramifications, until 

 they at last disappear from view in the form of the finest fila- 

 ments. The finest lateral filaments were regarded as primi- 

 tive fibrillar of the axis cylinders (Deiters), but hardly with 

 accuracy, for all is here obscure. 



Together with this system of processes — they have been 

 called protoplasma processes — we also meet with a long pro- 

 cess, which is always single, and usually arises from the cell 

 body, more rarely from the origin of another thick offshoot. 

 It never ramifies, and is conspicuous from its sharper, homo- 

 geneous appearance. This is the axis-cylinder process (a). 

 Later it is invested by the medullary sheath, and becomes a 

 nerve' fibre. This has also, however, been recently doubted 

 (Golgi). 



In the sympathetic of the frog Beale and Arnold met with 

 an interesting, although not yet accurately determined struc- 



