194 DISSECTION OF THE BRAIN. 



of Rolando, 1 R. Its under part, which rests on the orbital plate, has been 

 called the orbital lobule. 



The parietal lobe (Par, fig. 60) is placed behind the preceding, and 

 reaches down to the Sylvian fissure. It is about half as long as the fron- 

 tal. In front it is bounded by the fissure of Rolando, R, and behind by 

 ^. the parieto-occipital (P 0}. The upper and hinder part, close to the 



O median fissure, is named the parietal lobule (o 7 ). 



O 





TS 



LOBES OF THB HEMISPHERE, ASD CONVOLUTIONS AND FISSURES OP THE OTTER SURFACE. 



Fr. Frontal lobe. 4, ascending frontal; and 



Pnr. Parietal lobe. 5, ascending parietal gyrus ; 



Oc. Occipital lobe. 6', parietal lobule; 



T S. Temporo-sphenoidal lobe. 6, angular gyrus ; 



R. Fissure of Rolando. 7, superior ; 



8. Posterior. 8, middle ; and 



'S. Ascending limb of the Sylvian fissnre. 9, inferior temporo-sphenoidal gyrus ; 



P 0. Place of the external parieto-occipital 10, superior; 



fissure which is not visible in a side 11, middle ; and 



view. 12, inferior occipital convolntion. 

 IP. Intra-parietal sulcus. A. Supra-marginal convolution 



P. Parallel sulcns or, first ; 



1, inferior ; 6, second ; 



2, middle ; and c, third ; and 



3, superior frontal gyrus; d, fourth, annectant gyrns. 



The occipital lobe (Oc, fig. 60) constitutes the pointed end of the hemi- 

 sphere, and measures about a fifth of the whole. In front it is separated 

 from the parietal lobe by the parieto-occypital fissure (P 0), but below it 

 blends with the following lobe. It rests on the tentorium. On the inner 

 surface is a triangular piece, the occipital lobule ( a , fig. 62). 



The temporo-sphenoidal lobe (T S, fig. 60) projects into the middle 

 fossa of the base of the skull. It is situate behind the fissure of Sylvius, 

 and below the parietal and occipital lobes. The outer surface is in contact 

 with the cranium, and the opposite is supported mainly on the tentorium. 



The central lobe or the island of Reil (C, fig. 61) lies in the sylvian fis- 

 sure, and is concealed by the overlapping of the frontal and temporo-sphe- 

 noidal lobes. On separating those lobes it will be seen to be bounded in 



1 By some the anterior limb of the fissure 'S is made the hinder bound of the 

 lobe ; but this is not so good an arrangement as that in the text. 



