464 HISTORY OF THE HUMAN BODY 



fishes the system is better developed in this region than in the 

 trunk. In the embryo also the cephalic portion develops be- 

 fore the rest. 



The system appears well developed in Amphibia, with its 

 two lateral trunks. In Sauropsida a pair of subsidiary trunks 

 in the neck region accompanies the vertebral arteries, the only 

 instance of a distinct dorsal position for any part of this system. 



From the ganglia as centers numerous nerve fibers proceed, 

 supplying many of the internal organs, especially the alimen- 

 tary canal and the arteries, the favorite mode of distribution 

 being an intricate plexus, which spreads over the broader sur- 

 faces and enwraps the smaller parts. 



Owing to the origin of the sympathetic system from the 

 strictly metameric sensory ganglia of the cerebro-spinal nerves, 

 this system also shows at first a metameric character ; this ap- 

 pearance becomes modified, however, in regions of the greatest 

 differentiation, as in the head and neck and the pelvic region. 

 The four cephalic ganglia, ciliary, spheno-palatine, otic, and 

 submaxillary , which in mammals assist in forming connec- 

 tions between certain of the cranial nerves, and which have 

 been treated with these latter parts, belong to the sympathetic 

 system. 



