CHAP, xi] Tujte of Fibre Arntiif/ciitnif 251 



The foregoing is a brief description of the conformation in a normal case; of course 

 variations occur, but these I need not enter into. 



For the purpose of specially studying the structure of the insula I have removed it 

 entirely from two brains and examined its nerve cells and fibres in serial transverse 

 sections. 



And now a word concerning territorial subdivision: I observe that Flechsig splits the 

 insula into four myelogenetic areas, the first lies behind the sulcus centralis insulae and 

 is classified " primordial," of the remaining three (all marked in front of the central sulcus), 

 one, situated towards the lower end of the gyms centralis anterior, possesses mixed " inter- 

 mediate" and "terminal" characters, while the other two pertain to the "intermediate" class. 



Next Brodmann 1 , from studies in cell lamination, divides the insula into three fields, 

 which he states are more readily defined during phases of development than in the adult 

 condition, but since, at the time of writing, Brodmann's full paper has not appeared I cannot 

 give the distribution of his areas. 



Lastly from my inspection of the adult cortex I have arrived at the conclusion that 

 although variations in different parts might allow of further subdivision it is sufficient, 

 especially as the structure is in no part particularly interesting, to describe the island as 

 consisting of two areas, an anterior and a posterior, and to make brief reference to variations 

 existing within these main subdivisions. 



TYPE OF FIBRE ARRANGEMENT. (Plate XXV, fig. 1.) 



In writing of the fibre arrangement of the insula, Kaes refers to it as exhibiting the 

 simplest form of development, and as resembling the formation met with in other parts of 

 the brain during the period of childhood. He incautiously adds that its fibre development 

 is impelled during embryonic growth by physical circumstances. As to the insular cortex 

 showing a simple type of fibre arrangement I am at one with Kaes (on the second point 

 want of experience prevents me from speaking) ; moreover, I believe that the topical variations 

 in fibre constitution of which I shall write are only slight changes from a main type, and 

 on the whole suggest an invasion of the insula by cortex from surrounding areas. The 

 fundamental formation may be described as follows : 



Zonal Layer. 



The zonal layer in all parts of the insula has an advantage in point of depth over 

 the layer in most other regions. Constitutionally, however, it is not particularly strong, the 

 great majority of its fibres are very delicate and varicose, coarse varicose fibres are uncommon, 

 and coarse evenly-medullated fibres rare. Representation is slightly better in front of the 

 sulcus centralis than behind: and in the region of the "pole 2 ," creeping up from the under 

 surface, indications of the exaggerated zonal layer of the hippocampal region are seen. 



1 From an abstract, in the AY/V//M<;I'.-//.'.< (.'rittralblatt, of his paper read before the Berliner Gesellsehaft fiir 

 Psychiatric und Nervenkninkheiten. 



2 The term "pole" is applied to the point where the three anterior insular gyri blend inferiorly. 



322 



