620 THE HUMAN BODY. 



medulla oblongata, but they are so mingled with other fibres 

 that they have not been satisfactorily traced. 



Passing now to the tegmentum, it is first to be borne in 

 mind that many fibres (including most of those of the anterior 

 cerebellar peduncle) entering it from behind, end in the large 

 red nucleus lying in its anterior portion and in its other gray 

 masses. From these (Fig. 178) numerous fibres, rn, pass to 

 the optic thalamus: so that the majority of the tegmental 

 fibres differ from the pedal in that they only have indirect 

 connection with the cortex through the thalamal and other 

 gray matter. The thalamus is united with nearly all regions 

 of the cortex by fibres, /, passing from its outer side into 

 the internal capsule, and distributed in special abundance to 

 the occipital lobe. Since the thalamus receives fibres through 

 the tegmentum from the anterior quadrigemina and the 

 lateral geniculata (which we have seen to bave close connec- 

 tion with the optic nerves), and there is independent reason 

 for believing parts of the occipital lobe to be closely associated 

 with visual perceptions, the close anatomical association of 

 that lobe with the thalamus is significant. Another group of 

 fibres, d, connects the thalamus with the temporal and occip- 

 ital cortex, but does not take its path through the internal 

 capsule. Some fibres of the tegmentum reach the cortex 

 without primary connection with the thalamus : of these is a 

 set, e, which passes through the lenticular nucleus (but with- 

 out any communication with its gray substance) on its way 

 to the frontal and parietal lobes. At ce is indicated a set of 

 fibres of the tegmentum which there is some reason to believe 

 run to the fore f>art of the cortex direct, having no connection 

 with the thalamus and passing ventral to the internal capsule. 



Most of the fibres of the fillet, we have seen, end in the 

 red nucleus or corpora quadrigemina: fibres arising in these 

 gray masses connect them with the thalamus and through it 

 with the cortex. 



Besides fibres connecting the cortex with other parts are 

 many which unite different cortical areas directly. A vast 

 number (Ca, Fig. 177) cross the middle line in the corpus 

 callosum and are believed to join corresponding parts of the 

 two hemispheres. Others pass over in the small white an- 

 terior commissure and unite the two olfactory lobes and 

 portions of the temporal lobes. The posterior commissure 

 unites mainly the optic thalami and the front ends of the 



