FUNCTIONS OF THE BKAIN. 



805 



(5) The central lobe, or island of Reil, consists of five or six short, stra'ght 

 convolutions (gyri operti) radiating out and back from the anterior perforated spot, 

 and can only be seen when the margins of the fissure of Sylvius are separated. 



On the inner surface of each hemisphere is the gyrus fornicatus, or convo- 

 lution of the corpus callosum, which terminates posteriorly in the gyrus uncinatus 

 or gyrus hippocampi. Above is the marginal convolution, which is simply the 

 inner surface of the frontal and parietal convolutions, while the inner surface of 

 the ascending parietal convolution is termed the quadrate lobe, or precuneus.. 

 The parieto-occipital fissure terminates in the calcarine fissure and, running back- 

 ward in the occipital lobe, incloses the wedge-shaped lobule, — the cuneus. 



The importance of an acquaintance with the principal cerebral convolutions 

 as here sketched will be seen when the functions of the cerebral cortex are 

 considered. 



Fig. 347.— Left Side of the Human Brain (Diagrammatic). (Landois.) 



F frontal, P parietal, O occipital, T temporo-sphenoidal lobes ; S Assure of Sylvius ; S' h» ri ; on - 

 tal, S" ascending ramus of S ; c, sulcus centralis, or fissure of Rolando ; A ascending frontal and B 

 ascending parietal convolutions ; Fi superior, F* middle, and F 3 inferior frontal convolutions ; A 

 superior and / 2 inferior frontal fissures; / 3 , sulcus fraecentralis: P, superior parietal lobule; P2> 

 inferior parietal lobule, consisting of Po, supramarginal gyrus, and Po/, angular gyrus ; ip, sulcus inter- 

 parietalis ; em, termination of calloso-marginal fissure ; 0\ first. 2 second, Og third occipital convolu- 

 tions; po, parieto-occipital fissure: o, transverse occipital fissure; 02, inferior longitudinal occipital 

 fissure; Ti first, To. 

 sphenoidal assures. 



ijiitnl 

 > second, 



T 3 third temporo-sphenoidal convolutions; *i first, t% second temporo- 



In most ruminants the convolutions are arranged in the form of 

 parallel folds, extending from the front to the back of each hemisphere, 

 but are much more complicated than in the carnivora, where the surface 

 of the hemispheres is divided into four pairs of antero-posterior convo- 

 lutions, distributed around the upper end of the Sylvian fissure and 

 passing from the frontal to the parieto-teroporal lobe (Fig. 350). 



