530 Journal of Comparative Neurology and Psychology. 



part of the medulla oblongata, although its deep origin is ventral 

 (fig. 13). Soon after its emergence it comes into intimate relation 

 with the gasserian ganglion and more anteriorly with the ramus 

 ophthalmicus profundus V, for some distance being embedded in 

 the median border of these structures (figs. 13 and 6). Passing 

 through its own foramen in the skull (fig. 5) it runs a short dis- 

 tance to the vicinity of the origins of the eye-muscles and there 

 divides into two branches, the dorsal of which supplies the superior 

 rectus muscle, and the ventral the inferior and internal rectus and 

 the inferior oblique muscles (fig. 22). It will be seen (fig. 13) 

 that the dorsal branch passes dorsal to the main trunk of the 

 r. ophthalmicus profundus while the ventral branch runs ventral 

 to this nerve. The trochlear nerve, consisting of two or three 

 fibers, arises at the extreme posterior border of the dorsal part 

 of the mid-brain (figs. 13, 7 and 9) and passes anteriorly to its 

 foramen of exit closely pressed against the inner wall of the skull 

 (figs. 5 and 6). It ends in the superior oblique muscle (fig. 22). 

 The abducens is extremely attenuated. It takes its exit from the 

 ventral surface of the brain a little posterior to the level of the 

 origin of the seventh nerve as a few fibers, usually two in number 

 (figs. 7 and 13). These I have been able to follow but a short 

 distance. But anteriorly at the point where the r. mandibularis 

 of the fifth nerve leaves the gasserian ganglion (figs. 6 and 13) 

 there may be found leaving the ganglion or the r. mandibularis a 

 nerve of two fibers that passes out of the skull along with the 

 r. ophthalmicus profundus and ends in the external rectus muscle 

 (fig. 22). Before reaching the muscle the abducens nerve is 

 sometimes in very intimate relation with a small nerve that inner- 

 vates two small muscles which have their insertions upon the 

 antorbital cartilage. But there seems to be no exchange of fibers 

 between the two nerves. The incomplete development of the 

 eye-muscle nerves precludes any more extended account of their 

 relationships. Of ciliary nerves or ganglia I have found no 

 traces. 



5. THE TRIGEMINAL NERVE. 



a. The roots of the trigeminal nerve. — The fifth nerve derives 

 its fibers from four sources: (i) From the spinal V tract whose 

 fibers may be traced as far posteriorly as the level of the second 

 spinal nerve. (2) From fibers just dorsal to the spinal V tract. 



