SYMPATHETIC SYSTEM IN MAMMALS . 213 



II. HISTORICAL SURVEY 



The earliest observations on development of the sympathetic 

 nervous system are those of Remak ('47). That pioneer among 

 the investigators of the sympathetic system described the anlagen 

 of the sympathetic trunks in the chick as ganglionic enlargements 

 on the communicating rami, situated at their point of deviation 

 from the spinal nerves. He believed that the cells composing 

 these ganglionic enlargements are derived from preformed ele- 

 ments arising in the mesoderm. This view of the mesodermal 

 origin of the sympathetic nervous system held undisputed sway 

 for more than two decades, and has found advocates, among 

 whom may be mentioned Paterson ('91), in more recent times. 



The work of Balfour ('77) marks the beginning of our modern 

 conception of the ectodermal origin of the sympathetic nervous 

 system. According to his observations on the selachians, the 

 anlagen of the sympathetic trunks arise as simple enlargements on 

 the spinal nerve-trunks. Subsequently, these enlargements ad- 

 vance toward the aorta, each, however, retaining connection with 

 its respective nerve by a fibrous branch which becomes the com- 

 municating ramus. These ganglionic enlargements are at first 

 independent of each other, but become united later by longitudinal 

 commissures. These observations on the selachians were sub- 

 stantiated by Onodi ('86), Van Wijhe ('89), and Hoffmann ('99). 



Schenck and Birdsall (78) extended the conception of Balfour, 

 somewhat modified, to the higher vertebrates. Tracing the devel- 

 opment of the sympathetic trunks in birds and mammals, they 

 found that before the anlagen of the sympathetic trunks appear, 

 the spinal ganglia are not sharply limited distally. Groups of 

 cells become detached from the distal ends of the spinal ganglia 

 and advance far into the spinal nerve-trunks. These cells, they 

 believe, constitute the anlagen of the sympathetic trunks, but 

 they have given no clear conception of the process by which these 

 cells are transferred from the spinal ganglia to their new location 

 in the sympathetic anlagen. 



Kolliker ('97) adopted the doctrine of Balfour and attempted 

 to extend it to the peripheral sympathetic plexuses. In the ab- 



THE JOURNAL OF COMPARATIVE NEUROLOGY AND PSYCHOLOGY, VOL. 20, NO. 3 



