CHAPTER XL 



THE ISLAND OF RE1L. 



LARGELY on account of its unapproachable position the insula has not been fully explored 

 by the experimental physiologist and pathologist. From the anatomist and histologist, 

 however, perhaps unworthily, it has received much close attention. But in reference to the 

 histological work which has been centred on it, most seems to have been of the piecemeal 

 order, and although Kaes has investigated its fibre composition in a complete manner. 

 Brodmann its cell lamination equally thoroughly, and Flechsig has described the history of 

 its myelinisation, no individual worker, so far as I know, has carried out a conjunctive 

 and comprehensive study of its fibre and cell structure on the lines followed in the present 

 research. Hence, I think that no apology is needed for completing my survey of the cerebral 

 cortex with a chapter on this region. 



In order that my remarks on territorial variations may be free from ambiguity, it is 

 compulsory that I should open with an anatomical explanation, and at the outset let me 

 say that I propose to adhere to the terminology and description of the configuration of 

 the insula given by Eberstaller. As this observer states, the main bulk of the insula is 

 composed of five gyri, arranged in the form of a fan radiating towards the lower part or 

 limen of the island. Down the centre runs our principal and most constant guide, the 

 sulcus centralis insulae, placed in line with the fissure of Rolando above ; three of the 

 five gyri above-mentioned lie in front of this sulcus and two behind, they are individually 

 separated by lesser sulci, and are named in order from before backwards, 1. gyrus brevis 

 primus ; 2. gyrus brevis secundus ; 3. gyrus brevis tertius (gyrus centralis anterior insulae 

 of Cunningham); 4. gyrus longus (gyrus centralis posterior insulae of Cunningham); 

 5. gyrus posterior secundus. 



In addition to these, two minor gyri are described by Eberstaller, the gyrus transversus 

 and the gyrus accessorius, they are both placed in connection with the anterior insula ; 

 the gyrus transversus takes the form of an annectant and unites the lower end of the 

 gyrus brevis primus with the under surface of the frontal lobe ; the gyrus accessorius lies 

 a little higher and crossing the anterior limiting sulcus connects the insula with the orbital 

 operculum. 



As boundaries of the collection of gyri lying on this plane we have the anterior, 

 superior, and posterior limiting sulci, separating the insula from the orbital, fronto -parietal, 

 and temporal opercula, respectively, and in regard to the operculum last mentioned it is 

 important to recollect that the transverse gyri of Heschl do not form a portion of the 

 insula. 



