846 



THE NERVOUS SYSTEM 



which encloses the corpus callosum and the extremities of which approach each 

 other at the anterior perforated substance, where they are continuous with the 

 structures of the anterior portion of the rhinencephalon. The figure is bounded ex- 

 ternally by the sulcus cinguli above, by the subparietal sulcus (postlimbic sulcus) 

 and the anterior limb of the calcarine fissure behind, and by the collateral fissure 

 below. These respectively separate it from the frontal, parietal, occipital, and 

 temporal lobes. It comprises the following structures which are either wholly or in 

 part devoted to the functions of the olfactory apparatus: 



(!yrus cinguli (cingulum). 

 Isthmus of the gyrus fornicatus. 



/ hippocampal gyrus. 



Hippocampus " nc f; 



I dentate fascia. 



> fimbria. 



2. The medial and lateral longitudinal striae upon the corpus callosum. 



3. Thefornix. 



4. The corpus mammillare and thalamo-mammillary fasciculus to the anterior 



nucleus of the thalamus. 



5. Part of anterior cerebral commissure. 



6. Part of septum pellucidum. 



1. Gyrus fornicatus 



FIG. 628. DIAGRAM SHOWING POSITION OF STRUCTURES COMPRISING THE LIMBIC LOBE AS 

 SEEN FROM THE MESIAL ASPECT OF THE CEREBRAL HEMISPHERE. 



FOEXfX 



Til. \ LA MO-MAMMILLA R Y 

 l-'AfiClCULUH ( 17' -7 

 ll'AZYRl) 

 CORPUS MAMMILLA RE 



GYRUS CINGULI 

 MEDIAL AND LATERAL 



LOX<;1TU1)IXAL STRIDE 

 III' ftilll'CX r.l/./.o\r.V 

 .s /:// r.t/ PELL VCID UM 



HUBCALLOSAL GYRUS 

 1 1 1. FACTORY 11ULB 



MEDIAL OLFACTORY KTRIA 



LATERAL OLFACTORY STRIA 

 DENTATE FASCIA OR G YRUS 



The gyrus fornicatus comprises the greater mass of the limbic lobe. As seen 

 above, it is a term used to collectively represent a number of conjoined structures. 

 Being an incomplete ellipse in form, its two ends are united to form a closed ring 

 by means of the connection of the parolfactory area with the gyrus cinguli and the 

 connection of the anterior perforated substance with the uncus of the hippocampal 

 gyrus. It is best described in terms of its component parts. 



The gyrus cinguli begins in junction with the area parolfactoria below the anterior 

 end of the corpus callosum, and curves above so as to entirely embrace the upper 

 surface of the latter. It is separated from the frontal lobe by the sulcus cinguli 

 (calloso-marginal fissure), from the parietal lobe by the subparietal sulcus, and from 

 the corpus callosum below by the sulcus of the corpus callosum. By the latter 

 it is separated from the longitudinal strife of the upper surface of the corpus callosum. 

 The gyrus cinguli covers over, and its cells are closely associated with, the cingulum, 

 a well-marked band of white substance, which follows the gyrus backwards to turn 

 around the splenium of the corpus callosum, and then course forwards into the hippo- 

 campal gyrus to the uncus. The cingulum is largely recruited from the medial 

 olfactory stria and from fibres arising in the parolfactory area and the anterior per- 

 forated substance. 



The isthmus of the gyrus fornicatus is the constricted portion connecting the 

 posterior end of the gyrus cinguli with that of the hippocampal gyrus (fig. 619). It is 



