THE NERVOUS SYSTEM. 



419 



line. These finer and coarser fibres are partially intermixed, partly 



Fig. 161. 



disposed more in a fascicular manner, the 

 latter being the case near the ganglia of 

 the main trunk and in that part itself. 

 The structure of the ganglia is, in the 

 main, similar to that of the spinal ganglia. 

 Each of them consists : 1, of perforating 

 nerve-fibres, proceeding from one part of 

 the trunk to the other ; 2, of a certain 

 number of finer tubules originating in the 

 ganglion ; and 3, of numerous nerve-cells; 

 besides these the rami communicantes 

 also enter the ganglia, and a certain num- 

 ber of peripheral branches are given off from it. The nerve-cells in the 

 sympathetic (Fig. 162 B), present, in all essential particulars, precisely 

 the same conditions as those in the spinal ganglia, only that they are, 

 on an average, smaller, measuring 0-006-0*018, 0-008-0-01 of a line 

 in the mean, with less and paler pigment, or even colorless 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 preponderance of finer fibres), and, whether simple or com- 

 pound, 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, 



FIG. 161. Sixth thoracic ganglion, on the left side, of the sympathetic nerve of the Rabbit, 

 viewed from behind, treated with soda, and magnified 40 diam. : T. 2, trunk of the sympa- 

 thetic; R. c. It. c, rami communicantes, each dividing into two branches; Spl.,n. splanchnicus ; 

 S, twigs of the ganglion with two stronger fibres and finer filaments, probably going to 

 vessels; G, nerve-cells, and ganglion-fibres joining the main trunk. 



FIG. 162. From the sympathetic in Man, magnified 350 diam. : ./, a portion of a gray nerve 

 treated with acetic acid ; a, fine nerve-tubes ; 6, nuclei of the fibres of Remak. B> Three 

 nerve-cells, one with a pale process. 



