250 ALBERT KUN1Z 



Froriep's conclusion that the sympathetic neurones have their 

 origin in the ventral half of the neural tube and migrate out along 

 the fibers of the ventral roots of the spinal nerves is probably cor- 

 rect with regard to the neurones in the sympathetic trunks and 

 the prevertebral plexuses. I have shown, however, that the vagal 

 sympathetic plexuses arise from cells which migrate peripherally 

 along the fibers of the vagi. If, as experimental evidence indi- 

 cates, so ne of these plexuses contain sensory neurones, it is proba- 

 ble that these arise from cells which migrate from the vagus ganglia. 

 While it is impossible by direct observation to trace either sym- 

 pathetic excitatory or sympathetic sensory elements back to their 

 specific source in the cerebro-spinal nervous system, the facts at 

 our command warrant the conclusion that the sympathetic excita- 

 tory neurones arise from cells which migrate from the neural tube 

 along the fibers of the motor nerve roots, while the sympathetic 

 sensory neurones, wherever such neurones exist, arise from cells 

 which migrate from the cerebro-spinal ganglia. 



The nervous elements in the neural crest obviously have the 

 same origin as those which remain within the neural tube; they 

 are the descendents of the "germinal" cells of His. Retzius has 

 shown that in amphioxus sensory neurones are found lying near 

 the internal limiting membrane lining the slit-like central canal, 

 some of which send their dendrites out to the skin. In the fishes 

 also a relatively large number of cells remaining within the neural 

 tube give rise to sensory fibers which run to the skin. In embryos 

 of the salmon, according to Harrison, cells become separated from 

 the neural tube and, migrating ventrally, give rise to the spinal 

 ganglia. In embryos of the pig, as already indicated, medullary 

 cells migrate from the dorsal region of the neural tube into the dor- 

 sal nerve-roots. All these facts suggest that the cerebro-spinal 

 ganglia have arisen from cells which originally lay within the neu- 

 ral tube, and indicate the common origin of all sensory and motor 

 neurones. 



The orientation of the cells in the neural tube, during the period 

 of migration, is such that the cells which wander into the dorsal 

 nerve-roots seem to have their origin in the dorsal part of the 

 neural tube, while those which migrate into the ventral nerve- 



