82 Anatomical Considerations regarding Function [CHAP. 



and representing the " cortical lemniscus " was followed mainly into the ventral half of the nucleus 

 lateralis thalami, which was profoundly atrophied. Of course, as has already been mentioned, 

 the corresponding medial lemniscus was also atrophied. 



This very carefully studied case is of the greatest interest to us, not only because it gives 

 us much-needed information about the " cortical lemniscus " but because it strongly suggests 

 that the cortex of the postcentral gyrus is the end station of the sensory system of neurones, 

 and also that this station is much more limited in extent than others would have us believe. 



Other cases bearing on the subject are those recorded by Mahaim, the Dejennes, and 

 Jakob. In Mahaim's frequently quoted case, and also in Jakob's, the lesion was a primary 

 defect of both central convolutions ; while the Dejerines examined nineteen hemispheres in 

 which there was an old-standing destructive lesion in the Rolandic area 1 . In all these instances, 

 more or less profound alterations affected the lateral hypothalamic nuclei, and, in most, a secondary 

 retrograde atrophy of the medial lemniscus was observed. But while they all afford satisfactory 

 confirmation of the existence of an interrupting station in the thalamic region, they do not 

 satisfy our demand for knowledge concerning the course of the fillet from the thalamus to the 

 surface; and since in all, the lesion was distributed over both central gyri, they cannot be used 

 either for or against Tschermak's contention that this system of fibres is destined for the 

 postcentral gyrus only. 



Reflecting on the information concerning the pathway and destination of the " cortical 

 lemniscus " supplied by these studies of degenerations in both human being and lower animals, 

 one cannot refrain from expressing regret that the evidence is not more conclusive than it is, 

 and also that in previous years one has allowed to slip through one's hands material which 

 might have proved valuable in solving our problem. For although we have still to consider 

 the results of developmental findings, I feel sure that the path followed by this particular link 

 in the sensory chain will not be finally settled, until it is carefully studied in cases in which 

 it is in an active stage of degeneration. Now since it seems undeniable that the cells whose 

 axons compose this tract reside in the hypothalamic region, or inure accurately speaking in the 

 ventro-lateral group of nuclei of the optic thalamus ; and since for reasons some of which have 

 been already stated and others of which I shall emphasise later, it appears that the post- 

 central gyrus and particularly the Rolandic face of that gyrus is the cortical terminus of those 

 axons, it follows that the ideal lesion for the study of the degeneration would be one localised 

 in the ventro-lateral nuclei of the thalamus. But unfortunately the chance of obtaining a 

 case, say of softening, tumour formation or haemorrhage in the human subject, so limited as 

 to involve this part without complicating other structures is almost as remote as the possibility 

 of producing the necessary lesion artificially in one of the lower animals ; baulked in tins 

 direction, however, we could still turn and study the effects of a lesion in the opposite 

 extremity of the neuronic link, that is to say, in the postcentral gyrus. Of course in this 

 case we should have to produce a degeneration proceeding against the stream of physiological 

 conduction, which, if Waller's law were wholly true, would be impossible, but it was proved by 



1 It is mentioned by the Dejerines that atrophy of the medial lemniscus was not invariably present in their 

 cases, but it seems that the occurrence of such an atrophy is merely a question of time, for in several cases of 

 similar lesions of old-standing which have come under my own observation, and also in other cases recorded in the 

 medical press, reduction in volume of the medial lemniscus, wasting of internal arciform fibres, etc. have been outstanding 

 features. The atrophy is of course of a retrograde nature, affecting fibres thrown out of activity by the destruction 

 of the terminus on which the impulses they convey are projected, and its onset is quite in accordance with what we 

 know of retrograde degenerative manifestations affecting other systems of nerve fibres. 



