Cerebro-cortical Afferent and Efferent Tracts. 



3 



quaclrigeminal body and adjacent tegment. Those which 

 specially caused cutaneous anaesthesia were lesions involving 

 the reticular formation of the tegment of the pons and eras. 



In some of these cases there was no obvious loss of cutaneous 

 sensibility, while in "others this was pronounced. In both cases, 

 however, corticipetal degenerations were induced. These were traced 

 through both limbs of the internal capsule, the external capsule, and 

 the centrum ovale to the cerebral cortex, both on the convexity and 

 mesial aspect, including the gyrus fornicatus. This corticipetal 

 system is less extensive in the frontal than in the other regions of 

 the cerebrum. It would seem to harmonise with the thalamic corti- 

 cipetal fibres, which Flechsig has recently described as the first, 

 second, and third " sensory " systems, ascending respectively to the 

 Rolandic area, the falciform lobe, the frontal region and gyrus forni- 

 catus, myelinating at different periods. 



Many of these fibres of the tegmentum appear to pass through the 

 optic thalamus without ending in it, while others terminate in this 

 ganglion. This is shown by the fact that destruction of the lateral 

 and ventral parts of the optic thalamus led to a more extensive 

 degeneration than that following destruction of the tegmentum 

 alone, the fibres degenerating towards the same cortical regions. 

 But we have not been able to distinguish, by the degenerative 

 method, between those of sensation proper and the other afferent 

 fibres which ascend to the cortex in this region. 



Many fibres from the optic thalamus were found to cross by ihe 

 corpus callosum to the opposite cerebral hemisphere, thus supporting 

 the view of Hamilton that this structure is a decussation as well as 

 a commissure. Our observations show that the decussation is of 

 thalamic corticipetal fibres. 



(d) The other afferent cranial nerves, which were made the subject 

 of experiment, were the sensory division of the trigeminus,, 

 and the glossopharyngeus, which were divided proximal ta 

 their ganglia. 



Apart from degeneration of the so-called ascending trigeminal 

 and glossopharyngeal roots, traceable as far as the spinal-medullary 

 junction, no evidence was obtained as to their central continuation. 



But the symptoms following lesion of the tegmentum cruris placed 

 the sensory fibres from the face in association with those from the 

 body and limbs. 



(e) The experiments upon the prefrontal and frontal areas con- 

 firmed the existence of a fronto-pontine tract, which descends 

 through the anterior limb of the internal capsule and the 

 inner portion of the pes cruris to the pons Varolii. 



The subjects of experiment were exclusively monkeys. 



b 2 



