252 .journal of Comparative Neurology and Psychology. 



However, that the nerve cells upon the oculomotorius of Triton 

 and Amblystoma may be the source of sensory innervation of the 

 eye-muscles is merely a suggestion. Further work which I have 

 in progress may contribute something more positive upon the 

 question. 



2. N. Trochlearis. — The proximal, intracranial part of the 

 trochlearis is pressed down very closely upon the surface of the 

 brain, underneath or in the meninges, and is, for this reason, so 

 obscure that it might easily be overlooked in good dissections. It 

 passes out of the cranium either as a single nerve or in two divi- 

 sions. The latter condition, however, is probably rare, and when 

 it does occur the two divisions of the nerve fuse again before they 

 reach the m. obliquus superior, which the trochlearis innervates. 



As in Amblystoma, the trochlearis always comes in close rela- 

 tion with a branch of the ophthalmicus profundus. While it is 

 impossible to demonstrate any profundus fibers passing into the 

 trochlearis at this point, it is impossible also to assert that there is 

 not such an interchange of fibers. If the m. obliquus superior has 

 any sensory innervation this connection of the trochlearis would 

 seem to be the only possible course for the afferent fibers to enter 

 the profundus. In comparing this trochlearis-profundus con- 

 nection with the oculomotorius-profundus connections, it is mter- 

 esting to note that there have been no nerve cells found upon the 

 trochlearis. 



J. N. Abducens. — ^This nerve innervates the usual muscles, 

 rectus externus and retractor bulbi. That either of these muscles 

 ever receives any motor innervation from the fifth nerve is made 

 extremely improbable by the fact that in some instances the sixth 

 nerve does not touch the fifth at any point. In other cases, how- 

 ever, the sixth mingles with the ganglion cells of the profundus 

 ganglion so that the relation between the two nerves is very 

 obscure. In still other instances, a ganglionated branch of the 

 profundus, just beyond the ganglion, is observed to join the sixth 

 nerve. In one case of this kind, however, there seems to be a 

 passage of fibers from the sixth into the third nerve, and in this 

 particular instance the usual connective between the profundus 

 and the oculomotorius is wanting. This connective between the 

 sixth and fifth may, therefore, be only the commissure to the third 

 nerve. Yet in other cases, when no such connection with the 

 third nerve can be made out, there are ganglion cells on the sixth 



