490 Dr. A. W. Campbell. [> T ov. 17, 



Personal observations in three cases of Tabes Dorsalis, a disease affect- 

 ing the sensory system of neurones essentially, have disclosed profound 

 cortical alterations concentrated in this area. Similar observations in 

 cases of amputation of an extremity have revealed changes situated 

 on a corresponding surface level with those noted in the pre-central or 

 motor area. 



It is suggested that confusion concerning the function of the central 

 gyri has arisen in the past, from the fact that the tracts of fibres 

 pertaining to these gyri run in such close association below the Kolandic 

 floor, that a lesion affecting the conduction chain of one gyrus is rarely 

 free from the damaging influence of involvement of the other. 



Intermediate Post-central Area. This is a skirting zone in which the 

 structural type is intermediate between that of the post-central area and 

 the remaining parietal gyri. 



It may serve for the transmutation and further elaboration of 

 impressions primarily received in the post-central area. 



V. Visual Area. 



Cakarine or Visuo-Sensory Area. Two definite and distinct areas each 

 possessing a specialised type of cortex can be mapped out in the 

 occipital lobe. The distribution of the first is influenced by and bears 

 an extremely close relation to the calcarine fissure ; for the histologist 

 its chief feature is the well-known line of Gennari. 



Strong grounds exist for believing that this field is designed for the 

 primary reception of visual sensations, and of these the following may 

 be mentioned ; the only fibres in the occipital lobe possessing a 

 myelinic investment at the period of full fcetal maturation are those 

 proceeding to this area (Flechsig); clinico-pathologists have proved 

 that the minimal lesion equivalent to the production of a maximum of 

 blindness is one concentrated in the calcarine region ; it is possible to 

 map out this area from changes in it occurring as a result of old- 

 standing blindness (Bolton). 



Occipital or Visuo-Psychic Area. The second definable area forms an 

 investing zone or skirt to the first, and a remarkable wealth of nerve 

 fibres coupled with the presence of curious large pyramidal cells serve 

 for its identification. It is argued that this cortex is specialised for the 

 final elaboration and interpretation of sensations first received as crude 

 impressions in the calcarine area, and that its destruction is responsible 

 for those disabilities included in the category of psychic blindness. 



In the chimpanzee and orang analogous areas can be demonstrated, 

 but they extend much more widely on the lateral surface of the 

 hemisphere. 



