II50 



HUMAN ANATOMY 



dependent apex of the insula lies close to the anterior perforated space, with the 

 gray matter of which the cortical sheet of the island is continuous by way of 

 a transitional area, known as the limoi insidce, where the limiting sulcus of the 

 island is incomplete. In addition to being imperfectly separated from the surround- 

 ing opercula by the curved limiting sulcus (^sulcus circularis insulce^^ the islahd 

 is divided into an anterior and a posterior part by the sulcus cenh'alis ins^da;. 

 This furrow continues in a general way the downward and forward direction of the 

 fissure of Rolando, the deeper part of which is seen above the island (Fig. 991). 

 The anterior part, or preceiitral lobic/e, is subdivided by two, sometimes by three, 

 shallow grooves into three or four short downwardly converging ridges, the gyri 

 breves, of which the front one is connected with the deeper part of the inferior 

 frontal convolution by a small arched annectant gyrtis transversus. The hind-part 

 of the island, the postcentral lobule^ includes a longer wedge-shaped tract, the gyrus 

 lo7igiis, which below is continuous with the limbic lobe. The gyrus longus is 

 frequently subdivided by one or more shallow furrows into secondary ridges. 



The Limbic Lobe. — The limbic lobe (gyrus fornicatus) appears on the mesial 

 and inferior surfaces of the hemisphere (Fig. 987) as an elongated o-shaped tract, 



Splenium of corpus callosum 

 Callosal gryrus 



Fig. 992. 



Fornix, body 



Thalmus, partly cut away 

 Septum lucidum 



Fasciola cinerea' 



Calcarine fissure' 



Isthmu 



Rhinal fissure 



Uncus 



Collateral fissure 



Gyrus dentatus 



Gyrus Fimbria 

 hippocampi 



Portion of infero-mesial surface of left hemisphere, showing lower part of limbic lobe and adjacent structures. 



whose ends lie closely approximated with each other and with the anterior per- 

 forated space. These extremities are further intimately associated with the two limbs 

 of the olfactory tract, in this manner the limbic and olfactory lobes becoming, at 

 least topographically, continuous. The limbic .lobe comprises two parts, an antero- 

 superior and an inferior, of which the former, the callosal gyrus, lies concentric 

 with the upper surface of the corpus callosum, and the inferior part, the hippo- 

 campal gyrus, forms the mesial tract of the tentorial surface of the hemisphere. 

 The limbic lobe is separated from the adjacent convolutions by the calloso-marginal 

 sulcus in front and above, by the posdimbic sulcus behind, and by the anterior 

 part of the collateral fissure below. Its demarcation from the anterior part of the 

 temporal lobe is effected by the inconspicuous rhinal sulcus (fissura rhinica), or 

 incisura temporalis, which feeble furrow in man represents the important and 

 fundamental ectorhinal fissure of the lower animals. 



The callosal gyrus (gyrus cinguli), also called \\\& gyrus fornicatus (not to be 

 mistaken, however, with the same name as applied to the entire limbic lobe), begins 

 at the anterior perforated space, below the recurved rostrum of the corpus callosum. 

 Thence it winds around the genu of the latter and follows the convex dorsal surface 

 of the corpus callosum, separated however from it by the narrow callosal sulcus 

 (sulcus corporis callosi). On reaching a point ju-^t below the splenium, around which 



