.a 



178 SPECIAL HISTOLOGY. 



cells ; besides these the rami communicantes also enter the 

 ganglia, aud a certain number of peripheral branches are given 

 off from it. The nerve-cells in the sympathetic (fig. 162 B), 



present, in all essential 

 j _£ particulars, precisely the 



same conditions as those 

 in the spinal ganglia, 

 only that they are, on 

 an average, smaller, mea- 

 suring 0-006 — 0-01 8'", 

 0-008 — 001'" in the 

 mean, with less and paler 

 pigment, or even colour- 

 less and usually pretty uniformly rounded. As respects the origin 

 of the nerve-fibres of the main trunk, it is, in the first place, evident, 

 that they are in great part derived from the rami communicantes 

 which arise immediately below the spinal ganglia from the 

 trunks of the spinal nerves ; that they are in general formed 

 like the sensitive roots of those nerves (that is, contain a pre- 

 ponderance of finer fibres), and, whether simple or compound, 

 that they are manifestly connected with both roots. From all 

 that has hitherto been made out, the fibres of these connecting 

 branches are derived chiefly from the spinal cord and from the 

 spinal ganglia, and are consequently roots of the sympathetic ; 

 in a smaller proportion, however, they might be derived from 

 the sympathetic, and joining themselves to the spinal nerves 

 are further distributed peripherally together with them. Having 

 entered the main trunk of the sympathetic, the rami com- 

 municantes, so far as they are derived from the spinal nerves, 

 almost invariably run, dividing into two or several branches 

 upwards and downwards in it, towards its cephalic and pelvic 

 extremities, being in apposition with the longitudinal fibres of 

 the trunk. In the Rabbit, the fibres of a given ramus com- 

 municans may very frequently be traced as far as the nearest 

 ganglion and beyond it, in separate peripheral branches, but, in 

 general, the course of the individual fasciculi very soon escapes 

 the eye. It may nevertheless be asserted with great certainty, 



Fig. 162. From the sympathetic in Man, x 350 diam. A, a portion of a grey 

 nerve, treated with acetic acid ; a, fine nerve-tubes ; b, nuclei of the fibres of Remak. 

 B, Three nerve-cells, one with a pale process. 



