CRANIAL GANGLIA OF AMBLYSTOMA 493 



in the size of those cartilages when the crest cells were removed. 

 Although it was difficult to determine from the studies of normal 

 embryos what became of the neural crest migrating over the 

 dorsal and anterior margins of the optic vesicles, one case (fig. 81) 

 in which the crest cells were removed in the trigeminal region 

 seems to show conclusively that they form the anterior portions 

 of the trabeculae. This is in accordance with the findings of 

 Piatt ('97) and Landacre ('21). 



In no case do the crest cells enter into the formation of any part 

 of the branchial musculature as described by Goronowitsch ('93). 

 The musculature of the visceral arches is formed entirely from the 

 mesoderm of those arches. No portion of the skull other than 

 the anterior portion of the trabeculae is formed from the neural 

 crest. 



The only contribution of the neural crest to the formation of 

 cranial ganglia is probably to the general visceral portions of 

 VII, IX, and X. This conclusion is substantiated by the fact 

 that when the crest cells are removed from the branchial and 

 hyoid regions, there is a distinct lack of general visceral fibers, 

 while the gustatory, lateralis, and general cutaneous fibers are 

 normal. 



SUMMARY 



1 . Above the optic vesicle in early stages of Amblystoma there 

 is an elongated ophthalmic placode which gives off cells to the 

 formation of the ophthalmic ganglion. When the ectoderm in- 

 cluding this placode is removed as early as stage 23, the ophthal- 

 micus profundus V nerve and ganglion are absent. 



2. Near the anteroventral border of the supra-orbital lateral- 

 line primordium is a small gasserian placode of brief duration 

 which can be followed through stages 28 and 30. When a large 

 area of ectoderm is removed from the region posterodorsal to 

 the eye, deficiencies of the gasserian ganglion are produced. 



3. Lying close to the anterior border of the auditory placode is 

 a prominent placode elongated in a direction toward the dorsal 

 extremity of the hyomandibular cleft. It can be located as early 

 as stage 25. When ectoderm in this region is removed, even 



