THE DENTATE GYRUS. 



157 



It is a narrow convolution having a peculiarly toothed or notched appearance at its free 

 border, hence the name dentate. Above and overlapping it is the fimbria, from which 

 it is separated superficially by a shallow sulcus (fimbrio-dentate,f.f,-d.\ narrow in front 



. ,'>.: .*^ 



Fig. 110. DIAGRAM OF A SECTION THROUGH THE LEFT HIPPOCAMPAL REGION (E. A. S.) 



b.e., basis cerebri ; tr., tractus options ; n. o., nucleus caudatus ; /. rJi., fissura choroidea ; f., 

 firnbria ; f.f.-d., fissura fimbrio-dentata ; /. d., fascia dentata, /. Ji., fissura hippocampi ; //, hippo- 

 campus major; a., alveus ; e. coll., eminentia collateralis ; c. 1., cornu inferius ventriculi ; //, gyrus 

 hippocampi ; m., its medullary centre ; s.r.a., substantia reticularis alba ; /. coll., fissura collateralis. 



but broadening out behind, where it forms 

 a triangular depression below the splenium 

 of the callosum. The gyrus dentatus begins 

 posteriorly just behind and above the 

 splenium by a fine curved lamina (fasciola 

 cinerea), which is continuous with the 

 longitudinal striae (both lateral and mesial) 

 of the corpus oallosum (p. 127). From 

 here it bends downwards, lying along the 

 isthmus of the gyrus fornicatus and then 

 along the upper border of the hippocampal 

 gyrus ; .here the posterior pillar of the 

 fornix passes to its upper border in continuity with the fimbria (see p. 130). An- 

 teriorly it is continued into the cleft between the hippocampal gyrus and its uncus, 

 where it becomes lost to view. But if this cleft be opened out (fig. Ill) the dentate 

 gyrus is seen to exhibit a sharp curve within it, and in continuity with the curved 

 end a greyish band emerges from the cleft and passes transversely over the uncus 

 to disappear on the ventricular surface of that gyrus (Luschka, Giacomini). 



The part of the gyrus dentatus which lies below the splenium is sometimes much more 

 developed than usual, and shows strongly marked folds or dentations which recall the broad 



Fig. 111. HIPPOCAMPAL GYRUS AND FASCIA 



DENTATA, SHOWING THE CONTINUITY OF THE 

 LATTER WITH THE BAND OF GlACOMINI 

 PASSING OVER THE UNCUS. (Testllt.) 



