8o Journal of Comparative Neurology. 



3. The relation of the sympathetic neurons to — 



(a) the cerebro-spinal system ; 



(b) to other sympathetic neurons. 



4. Sensory fibers of the sympathetic system. 



5. Reflexes in the sympathetic system. 



Development of the sympathetic system. — The entire nervous 

 system, peripheral as well as central, has its anlage in a band or 

 plate of ectodermal cells, known as the medidlary plate, and 

 from the ectoderm in the immediate vicinity of this plate. Dur- 

 ing the further development of embryonic anlagen, the edges of 

 this plate become elevated to form the incditllary groove, and 

 the edges of the groove fuse to form the medullary canal, 

 which ultimately becomes completely separated from the re- 

 maining ectoderm. The ectoderm of the medullary plate, the 

 groove and the earlier stages of the canal, consist of a single 

 layer of cells. At a very early stage in the development of the 

 nervous system, indeed "before the groove has been converted 

 into a canal, a differentiation is noticed in these cells, two dis- 

 tinct forms being recognized. The one form, tall columnar 

 cells, which extend from one surface of the ectoderm to the 

 other, so-called spongioblasts, which develop, as has been clearly 

 shown, into the sustentacular tissue of the central nervous sys- 

 system, forming the ependym and neuroglia cells : and the 

 other form, large oval or round cells with prominent nuclei, 

 found between the spongioblasts ; these develop into nerve 

 cells and are known as germ cells. 



His (9) has shown that the germ cells proliferate very act- 

 ively by means of karyokinetic cell division and migrate from 

 a position near the inner wall of the medullary canal toward the 

 outer wall. While they are thus wandering, the round or oval 

 cell becomes pear-shaped and from the attenuated end there be- 

 gins to bud a process which is the anlage of a neuraxis. The 

 cells are now known as 7ienroblasts. 



The processes of many of these neuroblasts grow through 

 the ventral portion of the developing cord or brain and from 

 the anlagcn of motor roots. 



Many of the germ cells are therefore the anlagcn for the 



