252 G. E. COGHILL 



The ophthalmic trunk has grown considerably rostrad from 

 the ganglion (fig. 2, o.p.V), and follows a course in conformity 

 with the contour of the eye. It forms two divisions as it leaves 

 the ganglion, these representing, apparently, the two parts of 

 the gangUon that have been noted above. The larger of these 

 two nerves follows closely the contour of the eye to the immediate 

 region of the olfactory epithelium. Along its course several fila- 

 ments arise which penetrate the surrounding mesenchyme, with 

 the cells of which they become so intimately associated that they 

 very rarely can be traced continuously to the skin. From among 

 the mesenchyme cells, however, naked filaments emerge beneath 

 the skin and attach themselves to it. Such filaments are in all 

 probability the terminals of the n. ophthalmicus profundus. 

 They have the appearance of terminals of the Rohon-Beard cells 

 in the trunk, as described in' Paper I. It is possible that they 

 are processes from sensory neurones in the medulla oblongata 

 such as we have here under consideration. The smaller of the 

 two divisions of the N. ophthalmicus profundus passes more 

 directly forward (morphologically dorsad) and can be followed 

 only indefinitely in its distribution (fig. 2, i). 



The Gasserian ganglion still projects ventrad caudally of the 

 eye (fig. 2, G.G.), and dorsally of the primordium of the muscles 

 of mastication (fig. 15, G.G.). An infraorbital trunk now arises 

 from the extremity of the ganglion and extends at least two- 

 thirds of the distance across the lateral surface of this pri- 

 mordium (fig. 2, Mdb.). An occasional fiber arises from this 

 nerve and passes towards the skin, but no definite cutaneous 

 distribution can be made out for the nerve as a whole. 



The root fibers of the trigeminal nerve, upon entering the brain, 

 form an ascending and descending trigeminal tract (fig. 22, 

 Tr. asc.V,Tr.des.V). These apparently arise by a bifurcation of 

 the root fibers, although one can not be positive of this upon the 

 basis of the observations of individual fibers since the fibers are 

 very compact in their grouping. Figure 22 shows favorably the 

 extension of the trigeminal root fibers into the brain. The plane 

 of section may be interpreted from figure 16, which was made 

 from the same section. It will be seen to pass longitudinally 



