THE CEREBRUM 495 



continuous with the crus of the fornix below the posterior 

 part of the corpus callosum (p. 491). 



Fascia Dentata Hippocampi. The fascia dentata is 

 the free edge of grey matter which is placed between the 

 fimbria and the deep part of the upper surface of the hippo- 

 campal gyrus. The groove between it and the fimbria 

 is termed the fimbrio-dentate sulcus. Its margin is notched, 

 and its surface is scored with numerous closely -placed 

 transverse grooves. It begins posteriorly, in the region of 

 the splenium of the corpus callosum, and it runs anteriorly 

 into the cleft of the uncus, from which it emerges again in 

 the form of a delicate band, called the frenulum of Giacomini, 

 which crosses the recurved part of the uncus in a transverse 

 direction. 



Hippocampal Fissure. This is a complete fissure, and the 

 elevation on the ventricular wall, which corresponds to it, is 

 called the hippocampus (Fig. 217). It begins posterior to 

 the splenium of the corpus callosum, where it is continuous 

 with a shallow part of the callosal sulcus, and it passes 

 anteriorly, between the fascia dentata and the hippocampal 

 gyrus. Its anterior end is embraced by the uncus. 



SEPTUM PELLUCIDUM FORNIX TELA CHORIOIDEA 

 VENTRICULI TERTII. 



Septum Pellucidum. This is a thin vertical partition which 

 intervenes between the anterior cornua and the anterior parts 

 of the central portions of the two lateral ventricles (Fig. 198). 

 It is triangular in shape, and is prolonged posteriorly in the 

 narrow interval between the trunk of the corpus callosum 

 and the fornix, to each of which it is attached. Anteriorly, 

 it occupies the gap posterior to the genu of the corpus 

 callosum ; whilst below, in the narrow interval between the 

 rostrum of the corpus callosum and the fornix, it is prolonged 

 downwards to the base of the brain (Fig. 207). 



The septum pellucidum is composed of two thin laminae 

 which lie one on each side of the median plane. The median 

 cleft between the layers is termed the cavum septi pellucidi 

 (O.T. fifth ventricle] (Figs. 194 and 196). 



Dissection. The narrow middle strip of the corpus callosum, posterior 

 to the genu, should now be removed. Cut it transversely across, and, gently 

 raising it, separate the upper edge of the septum pellucidum from its lower 



