SPINAL NERVES IN VERTEBRATES 187 



course of the nerves to recall the arrangement found in Amphi- 

 oxus. In the region of the caudal heart clusters of these cells 

 were present in the dorsal sensory rami between the myotomes 

 and the median dorsal cartilaginous bar or at the point of branch- 

 ing of the nerve above the myotomes. Elsewhere not more than 

 one cell was found along the course of a sensory or a mixed spinal 

 nerve. These isolated cells were situated almost anywhere on 

 the main stem or branch. They appeared more frequently on 

 the dorsal rami than on the ventral, and very few of the abdomi- 

 nal or thoracic spinal rami possessed a peripheral nerve cell. 

 A tendency was noted for some of the spinal ganglion cells to 

 migrate a short distance into the nerve trunks, especially into 

 the dorsal rami. The peripheral nerve cells were apparently 

 bipolar, resembling in every particular the nerve cells of the 

 spinal ganglia. 



12. There is a similar distribution of peripheral ganglion cells 

 along the course of the vagus and glossopharyngeal nerves. At 

 the level of the caudal extremity of the mandibular muscles 

 these cells were sufficiently numerous in the vagus nerve to 

 constitute an elongated ganglion. 



13. The writer would regard the above mentioned peripheral 

 nerve cells, especially those of the spinal nerves, as representing 

 vestigeal ganglion cells of neural crest origin, which have mi- 

 grated peripherally along the nerve fibers, repeating in part a 

 more diffuse arrangement found in more primitive vertebrates 

 (Amphioxus). This xdew seems more tenable than to regard 

 them as the anlage of the sympathetic system; for the reason 

 that the peripheral spinal nerve cells are most numerous in the 

 extreme caudal nerves, more numerous in the dorsal than in the 

 ventral rami, very few appearing in the abdominal or thoracic 

 nerves, and in addition the cells are apparently bipolar, resem- 

 bling the structure and relationships of the ordinary spinal 

 ganglion cells. The vertebral and peripheral sympathetic sys- 

 tem of the higher vertebrates may arise from a further modi- 

 fication of this primitive migration process or it may have an 

 entirely independent but similar origin. 



