THE SYMPATHETIC SYSTEM. 199 



(Figs, in and 116 FS) : according to Gaskell a single nerve passes 

 from the first ganglion to the Ganglion nervi vagi, whence one 

 portion of its fibres is continued to the Gasserian ganglion, the re- 

 mainder accompanying the pneumogastric nerve without any con- 

 nection with the ganglion; he therefore names this nerve the 

 vago-sympathetic. (See Gasserian ganglion, p. 168.) 



c. Communications with the spinal nerves ; these are : 



(1) The Eami communicantes. 



(2) Communications between the sympathetic ganglia or their 

 branches and the spinal nerves or their branches (Fig. 117); by 

 means of these connections, fibres of the sympathetic system are 

 conducted by the spinal nerves and their branches to all parts of 

 the body. 



d. Branches to the heart, which form the following ganglia : 



(1) A relatively large plexus lies on the auricles in the median 

 plane immediately beneath the division of the J/. Jiyoglossus. It 

 supplies a network of fibres to the auricles and the adjacent large 

 vessels. It is said to communicate at various points with the 

 pneumogastric nerve. 



(2) A smaller ganglion of oval form, supplies twigs to the 

 neighbouring vessels and a communicating branch to the hypo- 

 glossal nerve (Wiedersheim). 



e. Branches to the abdominal viscera ; these form intricate 

 plexuses by which the organs are supplied : the one best known 

 is the solar plexus (Fig. 131) ; it is formed chiefly from branches 

 derived from the third, fourth, and fifth ganglia, and supplies 

 the stomach, etc. ; other plexuses for the various viscera are known 

 by corresponding names, such are the Plexus hepaticuz, renalis, geni- 

 talis, haemorrhoidalig, and xesicalis. 



The sympathetic system is characterised by the fact that the 

 branches form intricate plexuses, which include numerous ganglia 

 and which are very irregular ; it is also characteristic that most 

 of its fibres are non-medullated. According to the investigations 

 of Gaskell, the fibres of the sympathetic system arise in mam- 

 malia as very fine medullated fibres from the posterior vesicular 

 (darkens) columns (Mason has recently described cells in the 

 frog's spinal cord, which he holds to be homologous with the cells 

 of these columns) ; they leave the cord by both the ventral and 

 dorsal roots of the spinal nerves, and are thus connected with two 

 sets of ganglia, (i) with the ganglia of the dorsal roots, and (2) 



