THE NERVOUS SYSTEM OF AMPHIBIA 277 



is very indefinite in outline and has neither peripheral nor root 

 fibers arising from it. The lateral Une ganglia all have root 

 fibers connecting with the brain. Their peripheral ends reach 

 to the corresponding primordia of the lateral lines, excepting in 

 the case of the ganglion of the hj'omandibular system, the rela- 

 tion of which to the skin is very indefinite. The auditory vesicle 

 (fig. 73) is continuous with the skin and with the auditory gan- 

 glion. A barely perceptible auditory root connects with the 

 brain. The visceral sensory system is represented b}' the genicu- 

 late ganghon, the glossopharyngeal and vagus. All of these 

 connect with thickened patches of ectoderm which are associated 

 with the visceral pouches. The geniculate has a very small 

 root which reaches the brain. A strand of cells connects the 

 glossopharyngeal ganglion with the brain but no fibrillar ele- 

 ments appear in this. The vagus ganglion has no root. The 

 structure of the eye at this stage is illustrated in figure 72. The 

 olfactory epithelium has barely begun to invaginate and does 

 not yet touch the brain at the point of future origin of the olfac- 

 tory nerve. 



B. THE EARLY FLEXURE STAGE 



The ganglia of the trigeminal nerve have severed their connec- 

 tion with the skin and now have peripheral fibers which connect 

 obscurely with the skin (fig. 2). The root of the nerve forms a 

 very short ascending tract and a descending tract which, aug- 

 mented by neurones of the second order, extends to the level of 

 the auditory vesicle (fig. 22). The jugular ganglion of the vagus 

 has a very indefinite outline. It connects directly with the over- 

 lying skin but has no perceptible peripheral or root fibers. The 

 ganglia of the acustico-lateral system have acquired greater 

 definiteness of outline and compactness of structure. They now 

 send fibers to the various prunordia, with which they are still 

 in contact. Their root fibers enter the brain distinctly. The 

 auditory vesicle has become detached from the skin and from 

 the auditory ganglion (fig. 75). The visceral sensory ganglia 

 are still connected with the epibranchial placodes and no pe- 

 ripheral fibers arise from them. The root fibers of the geniculate 



THE JOURNAL OV COMPARATIVE NEUROLOGy, VOL. 26, NO. 3 



