72 THE CEREBRUM. 



may be seen separating the island from the frontal, parietal and 

 temporal lobes (Figs. 25, 26 and 36). The circular sulcus is 

 lacking only at the antero-inferior part, at the pole, where the 

 cortex of the island is continuous with that of the posterior orbital 

 gyrus and with the anterior perforated substance, and is on the 

 same level as the orbital area of the basal surface. The imaginary 

 line separating the anterior perforated substance from the island 

 is called the threshold of the island (limen insulce). 



In the island there is one named sulcus and four to six gyri 

 which have a radial or fan-like grouping (Fig. 25): 



Sulcus \ Central of the island (s. centralis insulae). 



. j Short (gyri breves), three or four of them. 

 ' \ Long (gyrus longus furcalis). 



The sulcus centralis insulce begins at the apex, or pole, of the 

 island and runs obliquely upward and backward dividing the 

 lobe into two lobules (Fig. 25). It is in the same transverse plane 

 as the central sulcus (of Rolando). In front of it, is the pre- 

 central lobule composed of the short gyri and continuous with 

 the frontal lobe; the post-central lobule lies behind it and is in 

 continuity with the parietal, temporal and limbic lobes. 



The gyri breves insulae, three or four in number, are separated 

 by shallow, furrows which diverge upward and backward from 

 the smooth apex of the precentral lobule (Fig. 25). They are 

 joined to the orbital operculum by a short annectant gyrus (gyrus 

 trans-versus insulce of Eberstaller} which extends from the apex 

 around the lower end of the anterior circular sulcus. Their 

 connection under the circular sulcus with the foot of the inferior 

 frontal gyrus suggests a participation in the speech center, and 

 they are figured by Mills in that center. However, the paraphasia 

 which results from lesions in the short gyri may be due to the 

 involvement of an association tract of fibers running underneath 

 them. 



Gyrus Longus (Fur.calis) (Fig. 25). It lies behind the central 

 sulcus of the island and trends obliquely backward and upward. 

 Posteriorly, it bifurcates for a short distance forming two short 

 branches which are continuous under the circular sulcus with the 



