CRANIAL GANGLIA OF AMBLYSTOMA 469 



is outlined from a case one day after operation (fig. 54). The 

 operation was done at stage 25 and the extirpated area included 

 the auditory placode as well as ectoderm anterior to it, although 

 its anterior extremity did not include as much ectoderm as in 

 the cases of the removal of the preauditory placode and supra- 

 orbital primordium already described. The ventral extension of 

 the extirpated area reached as far as the lower portion of the 

 hyoid arch and in a few cases the mesoderm of the hyoid arch 

 was exposed farther posteriorly than is the case in figure 54. 

 The extension of the blue area at the time of killing, twelve days 

 later, is shown in figure 55. All the groups of sensory lines are 

 present except the supra-orbital group, although the sense organs 

 which do appear on the right side of the head and lower jaw are 

 not as prominent as on the normal side. 



A reconstruction of the VII ganglionic components reveals 

 only a small portion of this ganglion on the operated side (figs. 

 56 a and b) . It lies lateral and slightly posterior to the ganglion 

 of V and is elongated in the dorsoventral axis. As near as can 

 be determined, a very slender root of fibers enters the brain near 

 the posterior border of the V. The lower extremity of this small 

 ganglion receives slender nerve fibers from the regions of lateral- 

 line sense organs on the side of the head and the ventral side of the 

 lower jaw. Xo palatinus, alveolaris, nor cutaneous portions of 

 the jugularis nerves can be found on the operated side as are 

 shown on the normal side (fig. 56 b). The ceratohyoid cartilage 

 is slightly smaller on the operated side. The ganglionic portion 

 of V in this indi\ddual seems to be concerned only with the oph- 

 thalmicus division. Another specimen which had a similar area 

 removed during stage 25 was killed nineteen days after operation, 

 and it also shows the same results. 



A similar operation upon an embrj^o at stage 26-27 shows a 

 small VII ganglion (fig. 57) . The fibers from it seem to be lateral- 

 line fibers to the sense organs on the lower part of the head. 

 There is distinctly no palatinus VII, and whether the other com- 

 ponents are entirely lacking or not cannot be exactly determined, 

 for the animal was killed within a few days after the operation, 

 and the small VII ganglion on the operated side has not developed 



