THE NERVOUS SYSTEM OF AMPHIBIA 259 



auditor}' vesicle, but within the brain these fibers have no per- 

 ceptible extension. 



2. The visceral sensory component of the facial nerve. The gan- 

 glion of this component, also consists of rather scattered cells 

 which occupy a position ventrally of the lateral line ganglia. 

 It projects laterad and ventrad to the ectodermal thickening 

 which is associated with the spiracular pouch (Paper I, fig. 56 

 Ec.Th.). With the cells of this thickening the ganglion is prac- 

 tically continuous. There are no perceptible nerve fibers in the 

 peripheral portion of the ganglion or arising from it to form a 

 nerve. Centrally there appear to be a few root fibers which 

 reach the brain, but it has so far been impossible to dififerentiate 

 them certainly from the other root fibers of the complex or to 

 establish that they are constantlj- developed at this time. 



3. The auditory nerve and vesicle. The auditory vesicle of this 

 stage has a broad attachment to the skin (fig. 73, Ad.,Aud.V). 

 This contact is with the lateral aspect of the vesicle. The endo- 

 lymphatic appendage (End.) is very imperfectly differentiated 

 from the rest of the vesicle, but it can be readily recognized. 

 The epithelium of the mesial, ventral and ventro-lateral regions 

 of the vesicle is still very thick, and mitosis is particularly abun- 

 dant in the more ventral portion. The ventro-mesial portion of 

 the vesicle is continuous with the auditory ganglion (fig. 73, 

 G.VIII). As the ganglion projects rostrad it become free from 

 the vesicle and a fiber or two from its proximal end reach the 

 brain at a point more ventral and caudal than the root connec- 

 tion of the lateral line ganglia with the brain. 



B. THE EARLY FLEXURE STAGE 



All the ganglia of this complex have acquired more definite 

 contours and greater compactness of structure. The interrela- 

 tions of the ganglia can be most favorably studied in frontal 

 sections; the root connections with the brain, in transverse 

 sections. 



1. The lateral line component. The two, distinct lateral fine 

 ganglia I distinguish as a and b (fig. 2, G.L.L.VII,a and b). The 



