Ckap. II.] 



A NEIIVOUS SYSTEM. 



35 



at all. They are to be regarded as single channels (however 

 devious their course rnay be), along each of which separate 

 stimulus-waves are capable of being transmitted. We can 



Fig. 7. — The Cervical Plexus, composed by interlacements of the last four cervica 

 (1, 2, 3, 4) and the first dorsal nerves (5). The various branches (6-21) are distributed 

 to the shoulder, arm, fore-arm, and hand. (Sappey after Hirschfeld.) 



* 



speak here only of probability, as this is a subject neces- 

 sarily beyond the reach of actual observation. 



Nerve Cells vary much in size and shape — the smallest 

 being about g^Q^-Qth, whilst the larger may be 3-^o^h of 

 an inch or more in diameter. They are more or less 

 granular bodies, each of which contains a large nucleus, 

 and within this an unusually distinct 'nucleolus' (figs. 

 1 and 8). Near the nucleus a heap of yellowish or 

 orange coloured pigment granules may often be seen. The 

 substance of the cell is continued into two or many ' pro- 



