THE CEREBRAL CORTEX. 



INSULAR 



ASSOCIATION 



AREA 



speak of as the inexcitable or latent portions, since they are dis- 

 tinguished from the rest by the fact that their excitation produces no 

 obvious response, and their excision no definite paralysis, their function 

 is at present a matter of conjecture. 1 What appears clear is, that any 

 A extensive lesion, es- 



pecially bilateral, of 

 these portions, leads 

 to alterations in the 

 intellectual condition 

 of the patient, altera- 

 tions which appear to 

 vary directly with the 

 amount destroyed. 2 

 These inexcitable 

 portions of brain sur- 

 face are chiefly massed 

 in the prefrontal, in 

 the post-parietal, in 

 the temporal, and in 

 man in the occipital, 

 regions ; to which 

 must be added the 

 cortex of the island 

 of Eeil. 



According to 

 Flechsig, the fibres 

 of the corona radiata 

 of all these parts be- 

 come myelinated far 

 later than those of 

 the excitable areas, 

 and very few of the 

 fibres pass downwards 

 as projection fibres, 3 

 but nearly all belong 

 to that class of inter- 

 FIG. 351. Diagrams to show the supposed division of the -nnnm'nl fiKvP wVn'nli 

 cerebral cortex into projection and association areas, the 



former being shaded with dots. A, lateral ; B, mesial sur- were termed associ- 

 face. Modified from Flechsig. alion fibres by Mey- 



nert, 4 from the fact 



1 An anatomical distinction between the excitable and latent areas consists in the fact 

 that whereas the latter all belong to the five-layered cortical type of Meynert, the excitable 

 regions, and to these must be added the gyrus fornicatus and hippocampal lobe, all possess, 

 either in addition to or in substitution for the usual five layers of cells, certain peculiarities 

 of structure, e.g. the giant cells of the Rolaudic area, the small stellate cells of the visual 

 area, the special features of the hippocampal region, etc. 



2 It must, however, be observed that this statement is probably true of the excitable 

 regions also. 



3 Dejerine, however, finds that the prefrontal lobe is united to the internal nucleus of 

 the thalamus by numerous fibres (Gompt. rend. Soc. de biol., Paris, 1897, p. 178) ; and other 

 authorities have come to a similar conclusion ("Versl. Deutsch. Naturf. u. Aerzte," 

 Neurol. Centralbl. , Leipzig, 1896, S. 995). Flechsig, ibid., 1897, S. 290. finds that the 

 internal nucleus of the thalamus is developed proportionally with the development of the 

 so-called association centres. 



4 Article "Brain" in Strieker's "Handbook"; also " Psychiatric, " Wien, 1884, 

 and "Neue Studien ueber die Associationsbiindeln des Hirnmantels," Sitsswngsb. d. k. 

 Akad. d. Wissensch., Wien, 1892, Bd. ci. 



