THE BRAIN 133 



The middle occipital convolution joins the angular convolution 

 by the second annectant gyms, and to the middle temporo- 

 sphenoidal convolution by the third annectant gyrus. 



The inferior occipital convolution is connected to the inferior 

 temporo - sphenoidal convolution by the fourth annectant 

 gyrus. 



On inner surface : 



The cuneate lobule is the area between the internal parieto- 

 occipital and the calcarine fissures. 



The calcarine fissure commences at the posterior part of the 

 inner surface of the occipital lobe by a forked extremity ; is 

 joined about half-way by the internal parieto-occipital fissure, 

 and ends near the posterior extremity of the corpus callosum. 



On under surface : 



The inferior occipito-temporal convolution lies just below the 

 collateral fissure, and extends from the apex of the temporo- 

 sphenoidal lobe to the posterior part of the hemisphere, form- 

 ing the under surface of both temporal and occipital lobes. 



4. The temporo-sphenoidal lobe : 

 On outer surface : 



The superior temporo-sphenoidal or parallel sulcus runs parallel 

 to posterior limb of the Sylvian fissure. 



The middle temporo - sphenoidal sulcus lies parallel to the 

 superior. 



The superior temporo-sphenoidal convolution (infra-marginal) is 

 bounded above by posterior limb of Sylvian fissure, and con- 

 tinuous behind with supra-marginal convolution. 



The middle temporo-sphenoidal convolution joins posteriorly 

 the angular, and by the third annectant gyrus merges into 

 the middle occipital convolution. 



The inferior temporo-sphenoidal convolution joins the inferior 

 occipital convolution by the fourth annectant gyrus. 



On under surface : 



Inferior occipito-temporal convolution in its anterior part. 



5. The central lobe or island of Reil lies in the fissure of 

 Sylvius at the base of the brain. Boundaries : In front, the 

 anterior sulcus of Reil, which separates it from the posterior 

 orbital convolution. Superiorly, the superior sulcus of Reil, 

 separating it from the gyri of the operculum, a collective 

 name given to the portions of the inferior frontal, and lower 

 ends of the ascending frontal and parietal convolutions which 

 lie between the ascending and posterior limbs of the Sylvian 

 fissure. Posteriorly, by the posterior sulcus of Reil, separating 

 it from the temporo-sphenoidal lobe. It is divided by the 

 central sulcus into an anterior part, which is subdivided into 



