CRANIAL GANGLIA OF AMBLYSTOMA 463 



eye, from which it was extended posteriorly to the incision on the 

 hj'-oid arch. The ectoderm thus outhned was very carefully 

 removed and the wound was covered by a graft of blue indif- 

 ferent ectoderm. 



A specimen killed six days after operation at a time when the 

 ophthalmic and gasserian ganglia have just fused at the point 

 of the entrance of the trigeminal root into the brain shows on the 

 operated side a somewhat smaller gasserian ganglion. The fron- 

 tal sections show that the ganglion in its anteroposterior diam- 

 eter varies little in the region near its root from that on the 

 •normal side, but as the ganglion is followed ventrally it soon be- 

 comes attenuated in the region near the upper posterior border 

 of the eye, while on the normal side the mandibular nerve does 

 not appear until the ganglion reaches the level with the middle of 

 the posterior border of the eye. The diminution in the size of 

 the gasserian ganglion is therefore represented mostly by a 

 shorter dorso ventral axis. A large portion of the ophthalmic 

 ganglion is displaced and lies near the anterodorsal portion of 

 the eye. A group of fibers connect it to ganglionic cells which 

 lie on the anterodorsal border of the gasserian ganglion. The 

 crest cells over the mandibular arch are apparently normal in 

 amount. 



Two other specimens killed the same number of days after 

 operation show the same results. In these cases, however, there 

 appears to be a slightly smaller number of crest cells over the 

 mesoderm of the mandibular arch. 



A control operation was also made on several specimens, in 

 which the ectoderm was excised in the usual manner and then 

 replaced and allowed to heal in its normal position. Sections 

 of these specimens show perfectly normal gasserian and pro- 

 fundus ganglia. 



It has already been shown (figs. 40 b and 43) that when the 

 ophthalmic placode was removed, including considerable ecto- 

 derm from the posterodorsal region of the eye, the gasserian 

 ^ .on was smaller than on the normal side. Among the cases, 

 described in another section of this paper, in which placodes of 

 VII were removed there appear two cases in which there is 

 apparently no gasserian ganglion present (fig. 56 b). 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 35, NO. 4 



