NOTES ON THE DEVELOPMENT OF THE NEWT. 247 



into the body^ but remains attached to the surface by a cord 

 of cells, which constitutes the dorsal branch (ophthalmic) of 

 the 5th nerve (fig. 24). At the same lime a nerve grows 

 down from the ganglion, which soon divides into two branches, 

 a posterior, the inferior maxillary, shown in figs. 24 and 26, 

 and an anterior, the superior maxillary, shown in fig. 24. 



The Facio-auditory nerve grows downwards towards 

 its corresponding sensory thickening, and fuses with it at two 

 points, one behind the other. The anterior of these we 

 interpret as the sense organ belonging to the 7th nerve, and 

 the posterior as the ear. There is only a very short distance 

 between them, along which the nerve is not fused. In a later 

 stage, shown in fig. 37, the ear is seen to be clearly distin- 

 guishable from the sense organ of the 7th nerve, the ganglion 

 of which is still fused with the skin, while the ear itself is 

 completely separate, forming a simple closed vesicle (fig. 36). 

 The main trunk of the 7th passes on downwards, and fuses 

 with the epiblast of the dorsal wall of the first visceral cleft 

 (figs. 37 and 36). Afterwards, this second connection with 

 the epiblast is lost, and the nerve divides into two bi'anches, 

 one behind and one in front of the first cleft (figs. 26, 31, and 

 32) . At the same time the ganglion on the upper part of the 

 trunk has sunk deeper into the body, remaining attached to 

 the sensory thickening by a cord of cells constituting the 

 dorsal branch (ophthalmic) of the 7th nerve (fig. 31). 



The facio-auditory nerve is now attached to the brain by 

 two roots, one behind the other; the anterior is shown in 

 fig. 26, and its connection with the ganglion and prse- and 

 post-branchial branches shows it to be the 7th nerve-root j 

 the posterior passes into the walls of the auditory vesicle 

 (fig. 31), and is therefore the 8th nerve. 



The 9th nerve fuses with its corresponding sensory epithe- 

 lium soon after its origin (fig. 27). The main trunk then 

 passes on and fuses with the epiblast of the 2nd gill-cleft, as 

 shown at a later stage in fig. 28. The root by this time has 

 shifted downwards from the dorsal surface of the brain. The 

 subsequent course of events is exactly the same as in the case 



