The Cerebtum. 427 



wards, some of the fibres, especially those for pain and 

 temperature, probably decussating at the different levels 

 of the cord, while others those for common sensibility 

 decussate at the upper part of the medulla. These pass 

 up in the medial lemniscus to end in the optic thalamus, in 

 which a higher neurone system begins, to end in the cor- 

 tex. The sensory path passes up through the tegmentum 

 of the crus, and, along with those fibres that have been in- 

 terrupted in the thalamus, enter the internal capsule, oc- 

 cupying the posterior third of the posterior limb, as men- 

 tioned above, to terminate in the gyrus fornicatus or in 

 the hippocampal region. While distinct partitions for 

 motor and sensory fibres would apparently exist from the 

 above description, in the internal capsule, yet it is alto- 

 gether likely that these tracts are more or less intermixed. 

 Behind the general sensory path in the capsule is the 

 visual tract, which connects the optic thalamus with the 

 cortical centres for vision. Next to this visual tract is the 

 acoustic tract for the temporal lobe, and, lastly, behind the 

 latter, the olfactory tract for the hippocampal region. 

 (Fig. 12.) In addition to these tracts, the internal cap- 

 sule contains projection fibres that go to the caudate and 

 the lenticular nuclei, along with fibres that pass between 

 these bodies, and still others that are connected to the 

 nuclei in and below the optic thalamus. 



Pressure Symptoms of Tumors of the Brain, 

 General symptoms. Headache is probably due to disten- 

 tion of the dura mater with resultant impression on the 

 fifth nerve that supplies this membrane. It can hardly be 

 caused by pressure on the cerebral tissue itself, since 

 M'ajendie has shown that the cerebral tissue is non-sensi- 

 tive. A tumor involving the cerebellum is often accom- 

 panied by constant, severe pain because of the limited 

 space this portion of the brain occupies, viz., the posterior 



