ORIGIN AND DISTRIBUTION OF THE NERVES. 139 



bution are the same as those of the plantar nerves of the fore 

 extremity. The second popliteal nerve passes between the 

 bellies of the gastrocnemii, above the first, detaching twigs 

 to them in its passage, and then spreads into many branches, 

 which penetrate the heads of the flexor muscles of the foot, 

 and sends filaments into the stifle joint. 



SYMPATHETIC NERVE. 



This nerve derives its name from the universal influence 

 which it has on the nervous system. It communicates with 

 the head, neck, chest, pelvis, and abdomen, by its frequent 

 intercourse and connection with their respective nerves. It 

 is supposed by some writers to be a nervous system of itself. 

 It has, at different distances, a great number of gangliform 

 tubercles, from which ramifications proceed forward, as well 

 as filaments backward, to the ganglia of the nerves of the 

 medulla spinalis. It is considered generally as beginning 

 from a branch of the fifth and sixth pair, given off at the 

 base of the cranium. The ganglionic structures, and the dif- 

 ferent plexuses are named from their form, location, and distri- 

 bution ; hence we have the cervical ganglion, semilunar, 

 sacral, &c. From the semilunar ganglion nervous filaments 

 shoot in various directions, which, from their being compared 

 to the rays of the sun, are denominated the solar plexus. From 

 the divergent filaments of the latter, the several smaller plex- 

 uses of the abdomen may be said to derive their formation, 

 taking names according to the viscera they are particularly de- 

 signed to furnish with nerves ; hence we have the splenic 

 plexus, that sends filaments to the spleen, the hepatic plexus, 

 mesenteric, aortic, hypogastric, and renal plexuses. The sym- 

 pathetic nerve in the abdomen travels over the sides of the 

 bodies of the lumbar vertebrae, beloAv the articulations of the 

 ribs, and pursues its course into the pelvis. Here, also, it 

 forms ganglia, which correspond in number to those of the 

 lumbar nerves ; and from every ganglion come off two fila- 

 ments ; one which runs to the corresponding lumbar nerve ; 

 the other crosses the aorta, and by joining the aortic plexus, 



