NOTES ON THE DEVELOPMENT OF THE NEWT. 245 



the epiblast in the region of the neural ridge^ but remains 

 connected with it in the median dorsal line behind the ridge, 

 while still further back the closure of the neural canal is not 

 yet complete. The neural ridge now extends through the 

 head (fig. 16) and the anterior part of the trunk (fig. 13). 



It may be here stated briefly that, as far as our observations 

 extend, the development of the spinal nerves is perfectly 

 normal. The neural ridge is prolonged at regular intervals 

 into nerves, which grow down between the medullary canal 

 and muscle-plates. The upper part of each nerve developes a 

 ganglion, and the ventral root is formed later, whether as an 

 outgrowth from the medullary canal or from the ganglion we 

 are unable to say. 



After our discovery of the neural ridge, we found that we 

 had been so far anticipated by Bedot (5), who described in 

 detail the development of the spinal nerves in the Newt. Our 

 observations only confirm his on this point. 



The Cranial nerves, like the spinal, arise as paired lateral 

 outgrowths of the neural ridge, being completely separate from 

 the epiblast. Figs. 17, 18, and 19 illustrate those outgrowths, 

 which give rise respectively to the 3rd, 5th, and 7th nerves. 

 The 7th and 8th nerves are at first fused, and the common 

 rudiment may be called, for convenience of description, the 

 Facio-auditory nerve. 



The Trigeminal nerve (fig. 18) is an outgrowth from 

 the dorsal surface of the brain, and is directed outwards and 

 downwards towards a lateral thickening of the epiblast, which 

 is cut transversely on one side of the section, and more 

 obliquely, so as to appear longer, on the other side. 



The Facio-auditory has the same relations to the brain 

 as the Trigeminal, and, like it, is directed outwards and 

 downwards towards a lateral epiblastic thickening. The 9th 

 nerve grows out similarly towards a corresponding epiblastic 

 thickening. These thickenings are situated slightly above the 

 level of the notochord, and are destined to give rise to the 

 mucous canals of the head. It will be most convenient to 

 take the future history of the nerves separately. 



