FUNCTIONS OF THE BRAIN. 



805 



(5) The central lobe, or island of Reil, consists of five or six short, straight 

 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 prseeuneus. 

 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.) 



Y frontal, P parietal, O occipital, T temporo-sphenoidal lobes ; S fissure of Sylvius ; S' horizon- 

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

 ascending parietal convolutions: f\ superior, Fo middle, and F 3 inferior frontal convolutions; f\ 

 superior and / 2 inferior frontal fissures; /s, sulcus fraecentralis : P, superior parietal lobule; Pg, 

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

 parietal is ; cm, termination 01" calloso-marginal fissure; Oi first, Oo. second, O ? third occipital convolu- 

 tions; po. parieto-occipital fissure; o, transverse occipital fissure; o 2 , inferior longitudinal occipital 

 fissure; TI first, T 2 second, T 3 third temporo-sphenoidal convolutions; <j first, f 2 second temporo- 

 sphenoidal fissures. 



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 S3^1vian fissure and 

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



