248 G. E. COGIIILL 



The first paper of this series, "The Afferent System of the 

 Trunk of Amblystoma," was pubhshed in Volume 24, number 2 

 (1914), of this Journal. It will be referred to in this communica- 

 tion as Paper I. In it (p. 163) were described the four physio- 

 logical stages of development upon which this paper, also, is 

 based. The next paper of the series will deal with the neurones 

 of the second and higher orders in the reflex arcs of the brain 

 and spinal cord. 



I. THE ANATOMICAL PART 



This part of the paper involves a rather detailed description 

 of the sense organs and sensory nerves of the head. This de- 

 scription, however, is not exhaustive, and may require supple- 

 menting as the study progresses. Readers who desire an even 

 briefer treatment of this phase of the subject may turn to the 

 summary of this part of the paper (p. 276) and to the figures, in 

 connection with which salient anatomical features are mentioned. 



1. The trigeminal nerve 



A. THE NON-MOTILE STAGE 



In embryos of the non-motile stage the ophthalmic ganglion 

 and the Gasserian ganglion are situated widely apart and come 

 into relation with each other only through their roots as the latter 

 approach the brain. The double nature of the trigeminal nerve, 

 therefore, is very obvious. As shown in figure 1, the ophthalmic 

 ganglion already extends forward over the eye and the Gasserian 

 ganglion extends ventrad behind the eye. 



The ophthalmic ganglion is directly continuous with the skin 

 near its rostral end (figs. 1 and 7 to 10, Ad.,G.oph.). Favorable 

 plane of section reveals two rather distinct portions of this gan- 

 glion (figs. 10, 11, 12, G.oph.a,b), and, at least in some specimens, 

 each part has an area of adhesion with the skin. Two such 

 areas are indicated in figure 1 (Ad.G.oph.). 



No peripheral distribution of fibers from the ophthalmic gan- 

 glion to the skin can be made out at this stage. The neuro- 

 blasts of the ganglion are bipolar and have perceptible axone and 



