474 L. S. STONE 



Another specimen killed twenty-two days after operation shows 

 all cartilages present, but slightly smaller in their dorsal portions 

 while their lower portions are normal. Posterior to the ear there 

 is but one occipital organ which is innervated by a single fiber 

 coming from a small group of ganglionic cells — possibly the X 

 ganglion. This ganglionic mass is very small and fused against 

 a small vagus ganglion which is apparently only a visceral gan- 

 glion. Motor fibers may be seen issuing from the region of this 

 ganglion to the branchial muscle. From the ventral side of this 

 vagus ganglion a few short fibers extend to the region of blood 

 vessels, where they are lost. Only the first branchial trunk of 

 the vagus can be found and it contains only motor and general 

 visceral fibers. The visceral trunk of the vagus ganglion may be 

 seen issuing from the posteroventral portion of the ganglion 

 (fig. 67). It carries no lateralis fibers, but is composed of general 

 visceral fibers which are lost in the posterior region of the pharynx. 

 The vagus lateral-line ganglion is entirely absent. No visceral 

 ganglion of IX can be found. 



These cases are typical of the findings from a study of a large 

 number of individuals and the results seem to show that whenever 

 the lateral-line placodes are removed no lateral-hne ganglia are 

 present, and when the ectoderm is removed from so large an area 

 as to include the epibranchial placodes of IX and X and surround- 

 ing ectoderm no sensory fibers of the cutaneous and the special 

 visceral system are present, while on the other hand the general 

 visceral component is derived from the neural crest. 



B. Removal of neural-crest cells 



1. Contribution to mesodermal tissue. The neural crest was 

 exposed to view by a longitudinal incision in the ectoderm begin- 

 ning at a point below the middle of the third somite in the antero- 

 dorsal border of the pronephros and extending cephalad through 

 the ectoderm of the dorsal third of the eye to the midhne. The 

 posterior extremity of the longitudinal incision was extended 

 dorsally to the middorsal line, slanting slightly caudad. The 

 ectoderm thus outlined was flexed dorsally hinging on the mid- 

 dorsal Une. 



