iv] Poxtceiitrol or Sensor;/ Area 81 



in the hypothaJamic region, as well as l>v pronounced atrophy of the medial lemniscus; and 

 although he has not been able to give us a clear idea of the course of the cortical division 

 ot this fibre system, he has established its existence by proving that the integrity of the 

 ponto-bulbar division of the same system is dependent upon a sound condition of the cortex. 



Attempts to trace the " cortical lemniscus " by degenerative methods in the lower animals 

 (dog, cat and monkey) have not been wholly successful. Von Monakow, Mott, and others, 

 after division of the lemniscus in its pontine or medullary course, were unable to follow the 

 subsequent ascending degeneration beyond the hypothalamic station, and Tschermak alone has 

 obtained positive results. The cat was the animal chosen by Tschermak, and after describing 

 the degeneration up to and about the thalamic region in the greatest detail, he goes on to say 

 that a number of scattered degenerated fibres passed out through the internal capsule and the 

 laminae medullares of the lenticular nucleus into the corona radiata, to finally stream up to 

 the cortex over an area of considerable extent lying behind the fissura coronalis. This area 

 Tschermak looks upon as the equivalent of the human gyrus postcentralis, in accordance with 

 Meynert's contention that in the cat, the sulcus coronalis, and not the sulcus cruciatus, is the 

 homologue of the fissure of Rolando. Tschermak 1 s work bears the stamp of thoroughness and 

 is favourably commented upon by those qualified to criticise, and it would suit my views to 

 accept his results without reserve. At the same time, however, we must remember that the 

 human being is a long way removed from the cat, and though it may be true that in this animal 

 a large proportion of fillet fibres proceed direct from the posterior column nuclei to the cortex, 

 without interruption in the thalamic region, it would be unsafe to infer that the same obtains 

 in the human being; indeed Mott's contrary experience in the case of the monkey and also 

 Horsley's go some way towards preventing this assumption. The work of von Vejas, and Singer 

 and Miinzer might be quoted in this connection, but I think enough has been said to show 

 that, up to date, the study of degenerations in the lower animals has been inadequate to the 

 determination of the exact course of Monakow's " cortical lemniscus." 



We are therefore obliged to turn for information to accounts of degenerations affecting 

 tli is region in the human being, and fortunately there are cases on record, now almost classical, 

 which afford instruction. Foremost we have the well-known case worked up by Hosel in 

 Flechsig's laboratory, one of a porencephalic lesion chiefly involving the postcentral gyrus of the 

 left hemisphere, in which the discovery of secondary changes in the medial lemniscus, traceable 

 downwards as far as the posterior column nuclei, originated Flechsig and Hosel's now exploded 

 view that these nuclei were brought into relation with the postcentral cortex by a single, that 

 is to say, uninterrupted tract of neurones. Now it is interesting to find that Tschermak, to 

 whose experimental work in this direction I have already referred, was given the advantage of 

 restudying Hosel's original specimen, and as he paid particular attention to the supposed 

 connections of the " cortical lemniscus " his observations are well worthy of special notice. The 

 old-standing surface lesion is described as involving the whole of the ascending parietal convo- 

 lution, spreading upwards over the paracentral lobule, and reaching as far as the insula in the 

 downward direction, and also extending slightly on to the upper extremity of the ascending 

 frontal and superior parietal gyri ; in association with this there was some destruction of the 

 underlying white substance. From this lesion a strand of degenerated fibres proceeded down 

 to the internal capsule, there to split into two parts, one of which was destined for the pes 

 pedunculi and was evidently a part of the motor tract (the corresponding motor bundles in 

 the pons, medulla and spinal cord had undergone degeneration), while the other of larger size 



c. 11 



