CRANIAL GANGLIA OF AMBLYSTOMA 483 



An examination of the specimens done at the earher stage 

 shows a deficiency of the mandibular and quadrate cartilages, 

 but not a complete absence. One case shows a deficiency in the 

 anterior portion of the trabecula. In the branchial and hyoid 

 regions it is quite evident that the branchial cartilages, the cerato- 

 hyal, the hyohyal, and the first basibranchial are derived from the 

 wandering neural crest. 



2. Contributions to ganglionic components, a. Contribution to 

 V and VII. As already shown in the cases described, there is no 

 condition in which the crest cells in the region of the trigeminus 

 were entirely removed, although in the other regions they have 

 been almost entirely eliminated. 



A specimen operated upon at stage 25 was killed two days 

 after operation and shows on the operated side a portion of the 

 ophthalmic placode which is giving off cells, even though few 

 crest cells may be found in this region. It lies close to the brain 

 (fig. 82) while farther ventrally placodal cells from the posterior 

 portion of the VII lateral-line placode are projecting medially 

 to form the lateral-line ganglion (fig. 83) . At its anterior portion 

 it is contiguous with a small group of cells which belong to the 

 gasserian placode. The epibranchial placode of VII at this stage 

 is prominent, but has split off no cells on either side. 



Although the crest cells have regenerated to a small degree in 

 the trigeminal regions of two other specimens killed within a few 

 days after operation, placodal cells may be seen contributing in 

 large numbers to an ophthalmic ganglion. The condition of the 

 ganglion is practically the same as on the normal side. One of 

 the specimens shows a large well-formed ophthalmic ganglion 

 (fig. 84), but the number of crest cells on the mesoderm of the 

 mandibular arch farther ventrally is far less than on the normal 

 side. Although there are but few crest cells on the mesoderm of 

 the hyoid arch of this specimen, the VII lateral-line ganglion is 

 present and normal (fig. 84). This level does not show the 

 comparative size of the two ganglia. The visceral portion of 

 the VII seems to be a Uttle smaller than on the normal side. 



Another typical case killed eleven days after operation shows 

 deficiencies in the mandibular group of crest cells and an entire 



