THE SYMPATHETIC DIVISION OF THE NERVOUS SYSTEM 153 



the phenomena of end disks and f enestrations signify regenerative activity. 

 They are relatively more abundant in regenerating transplanted ganglia. 

 But they are abundant also in pathological ganglia (Nageotte, 1906), 

 and in fetal ganglia (Huber, 1913). No conclusive evidence has yet been 

 presented that these modified forms signify functional derangement. 



THE SYMPATHETIC DIVISION OF THE NERVOUS SYSTEM 



The sympathetic division of the nervous system (autonomic system) 

 consists essentially of three sets of ganglia: (1) the ganglionated cords 

 (sympathetic trunks; vertebral ganglia); (2) the prevertebral plexuses; 

 and (3) the visceral or terminal plexuses, including chiefly the myenteric 

 and submucous plexus of the alimentary canal. The ganglia of the 

 ganglionated cords are segmentally arranged, and interconnected trans- 

 versely (caudally) and longitudinally by plexuses of non-medullated fibers. 

 They are connected also with the spinal nerves by the white and gray rami 

 communicantes. Homologous ganglia in the head region, less definitely 

 related to the cerebral nerves, are the ciliary, sphenopalatine, submaxillary, 

 sublingual, parotid and otic ganglia. The prevertebral plexuses represent 

 fusion products of originally segmentally arranged components correspond- 

 ing to segments of the ganglionated cord. These plexuses contain fewer 

 and smaller cells, with a preponderance of fibers, e.g., cardiac, celiac 

 (semilunar; solar), hypogastric and pelvic plexuses. The myenteric and 

 submucous plexuses are located in the muscle and submucous layers re- 

 spectively of the esophagus, stomach and intestine. Here the cells are still 

 smaller and less numerous than in the prevertebral plexuses, and the fiber- 

 network is less dense. A plexus is a network of nerve fibers with few cells ; 

 where the nerve cells are relatively abundant, the plexus is known as a 

 ganglion. The embryonal cells (neuroblasts) which develop into sympa- 

 thetic neurons have migrated from the neural crest, possibly in part also 

 from the wall, of the primitive spinal cord. 



Langley employs the term 'autonomic nervous system' for all that 

 portion of the peripheral nervous system not included among the cerebro- 

 spinal nerves, commonly designated as the 'sympathetic system.' This 

 comprises four components: (1) the sympathetic proper, including the 

 autonomic fibers arising from the thoracicolumbar regions of the spinal 

 cord, together with the associated vertebral ganglia and their postgang- 

 lionic neurons; (2) sacral autonomic, preganglionic fibers included in the 

 roots of the second, third and fourth sacral nerves, together with the asso- 

 ciated postganglionic neurons; (3) cranial autonomic, a group of fibers 

 arising from the midbrain and the medulla (this component is separated 

 from the sympathetic proper by the whole extent of the cervical region 



