532 THE CEREBEUM. 



extremity of the corpus eallosuni, and courses first forwards, then up- 

 wards, and then backwards, parallel with the edge of the longitudinal 

 fissure, and finally turns upwards to end at this edge just behind the 

 position of the upper extremity of the fissure of Rolando. It separates 

 the marginal convolution from the convolution of the corpus callosum, 

 hence its name. 



Convolutions. — The mnrgincd convolution commences in front of the 

 anterior perforated spot, and extends along the edge of the longitudinal 

 fissure as far as the termination of the calloso-marginal fissure at the 

 upper margin of this surface. Over this margin it is continuous with 

 the superior frontal convolution, and its continuation (straight convo- 

 lution) on the orbital surface. It is commonly broken up by secondary 

 fissures, one of which often runs parallel to part of the calloso-marginal 

 fissure. x\ secondary convolution not uncommonly connects it with the 

 next gyrus. 



The convolution of the corpus callosum, f/ijrus fornicatus (g. forn., fig. 

 373), commences near the anterior perlbrated spot, and, turning round 

 the anterior extremity of the corpus callosum runs backwards along its 

 upper surface, and then, bending down behind its posterior extremity, 

 takes the name of the uncinate convolution. On its outer side is the 

 calloso-marginal fissure as far as the latter extends. 



The quadrafc lohule (prascuneus), is a four-sided area lying between 

 the internal part of the parieto-occipital fissure behind, and the tenni- 

 nation of the calloso-marginal fissure in front. It is variously sub- 

 divided into small gyri, of which the highest is continuous with the 

 superior parietal lobule, and the lowest forms part of the gyrus forni- 

 catus. 



The cuneate lohule (occipital lobule) is a wedge-shaped area lying 

 between the internal parieto-occipital and the calcarine fissures. 



Occipito-teniporal region. — The convolutions of the lower part of 

 the occipital lobe and the inner temporo-sphenoiclal convolutions are 

 continuous, and may be considered together as three in number. 



The su]}enor occipito-temporal convolution {uncinate or hijipocampal 

 convolution) extends from near the posterior extremity of the hemisphere 

 to the anterior portion of the temporo-sphenoidal lobe, lying at first 

 beneath the calcarine fissure, and then beneath the dentate fissure. Its 

 anterior extremity is rounded into a hook called by Vicq-d'Azyr the 

 "crotchet;" hence its name. Beneath the posterior extremity of the 

 corpus callosum this convolution is joined by the gyrus fornicatus, in 

 front of the calcarine fissure. 



The inferior occipito-temporal convolulion has a similar extent and 

 parallel course, reaching through the occipital and temporo-sphenoidal 

 lobes of which it forms the lower margin. 



A miilille occi])ito-temporat convolution may be sometimes distinguished 

 between the two just described. 



The dentate or Mppocampcd fissure commences within the posterior 

 extremity of the gyrus fornicatus, which separates it from the calcarine 

 fissure. "Thence it extends downwards and forwards, ending below in 

 the notch of the uncinate convolution. Its floor is formed by grey 

 matter, called the fascia dentata (see p. 548). This fissure corresponds 

 to the elevation of the hippocampus major within the lateral ventricle. 



The coUcdcrcd fismre lies below the uncinate gyrus and parallel to the 

 calcarine and dentate fissures. It extends beneath the floor of the 



