152 Cincinnati Society of Natural History. 



the fibres within the brain is quite short and direct. The roots 

 break up at once into about twenty bundles, which enter obliquely 

 towards the median line, but very nearly in the frontal plane. 

 These fibre bundles may be separated into a number of groups, 

 which, however, are not well distinguished, and lie in the lamina 

 perforata posterior of either side. They can be traced dorsally to 

 a nucleus of large, nearly globular or polygonal cells with large 

 nuclei, forming a laterally-compressed aggregate on either side the 

 Sylvian aqueduct, extending upward and forward with an irregu- 

 larly ovate outline. 



A frontal section at the level of the third nerve passes through 

 about the middle of the colliculi (lateral projections of the ventri- 

 cles of the optic lobes.) (See Fig. 3, Plate XII.) 



No trace of a decussation of the fibres of the third nerve could 

 be discovered. 



On either side of the nucleus of the third nerve is a cluster of 

 multipolar cells with three or more acute prolongations, which may 

 be traced some distance towards the lateral margins. Although 

 the greatest prolongation is in the horizontal transverse direction, 

 yet horizontal sections show that they also connect with longitu- 

 dinal fibres obliquely forward and dorsad and backward and ventrad. 



An interesting band of coarse fibres can be traced from a decus- 

 sation below the aqueduct, obliquely upward across the tracts of 

 the third roots in a gently arched path to the extreme lateral bor- 

 ders of the nucleary zones at the angles of the ventricles of the 

 optic lobes. Here the fibres seem to pass to the colliculi with 

 those from the tectum opticum. Whether these fibres are the paths 

 of stimuli from the optic lobes to third root regions can not be 

 determined at present. (See Plate XIII , Fig. 9.) 



(4.) The patheticus (trochlearis) nucleus lies caudad and some- 

 what dorsad to that of the oculomotor. Its principal bulk lies in 

 the frontal plane, passing a little cephalad to the posterior margin 

 of the optic lobes. The fibres extend caudad and laterally, and 

 then curve to a prominent decussation just cephalad to the cere- 

 bellum. 



(5.) The fifth neme. The relations of the large and complex 

 trigeminal nerve have been imperfectly made out. There is, how- 

 ever, no difficulty in identifying the main motor nucleus, which 

 is reached by a strong direct fasciculus from the root, and occupies 

 a special protuberance into the fourth ventricle, which lies ventrad 



