176 FRED W. STEWART 



embryos, I am free to admit that I have been totally unable 

 to follow Kuntz' 'indifferent cells' back to their ultimate origin, 

 that is to a neural-crest origin as opposed to a neural-tube origin 

 — either one or both. The problem of the origin of the sympa- 

 thetic ganglia of the trunk region is less difficult. The path of 

 migration is for the most part shorter in the case of the sympa- 

 thetic ganglia which originate in relation to the spinal nerves 

 than it is for the cranial sympathetic ganglia; one must be 

 exceedingly cautious in accepting statements as to the definite 

 origin of neuroblasts apparently migrating along cranial nerve 

 trunks. We must for the time be satisfied in basing our interpre- 

 tation largely on future relationships, for at no time apparently 

 does one find a continuity en masse between the sensory ganglion 

 of the vagus and its sympathetic cells such as Held ('09), for 

 example, has figured for the trunk sympathetic. In addition to 

 Kuntz, Streeter ('12) indicates diagrammatically sympathetic 

 neuroblasts migrating peripherally along the vagus into the 

 cardiac plexus. 



In thirteen-day rat embryos the vagus has been traced caudad 

 to a point slightly below what has been considered the origin 

 of the superior laryngeal nerve. Within the next half-day the 

 vagus undergoes a rapid caudal extension and may be followed 

 into the condensing mesenchyme about the developing stomach. 

 Small but easily distinguishable neuroblasts are found massed 

 about the growing stump of the nerve and may be traced out 

 into a narrow strand of single cell thickness into the gastric 

 mesenchyme. The first distinguishable phase in the develop- 

 ment of the vagus portion of the sympathetic seems, then, the 

 grouping of neuroblasts about the growing tip of the vagus in 

 the lower esophageal region. In addition to these cells, an 

 occasional cell of larger proportions is encountered along the 

 vagus trunk ; these elements will be considered in later stages. 



For a considerable time the writer was at a loss to account 

 for the rapid increase in the number of neuroblasts along vagus 

 fibers and was inclined to search for large additions from the 

 trunk sympathetic ganglia. Careful search, however, failed to 

 reveal any trace of such contribution, and the true explanation 



