16 Anatomy of the Nervous System 



fimbria. The dorsal end of this (the postcommissural) part 

 of the hippocampal formation is connected posteriorly 

 through the gyrus subsplenialis with a narrow ridge, the 

 fasciola cinerea. This, in turn, curves round the splenium 

 of the corpus callosum and runs forward as the very thin 

 gyrus supracallosus or indusium griseum. All these struc- 

 tures are illustrated in PI. IV. 



Scraping away the gray matter, or cerebral cortex, from 

 the dorsal part of the hemisphere reveals the white fibres of 

 the corpus callosum, and this also may be removed so as to 

 expose the cavity of the hemisphere, the lateral ventricle. 

 The postero-medial part of the floor of the ventricle is formed 

 by a curved ridge, the hippocampus, while the small antero- 

 lateral portion appears as a convex mass, part of the corpus 

 striatum. Between these projects the chorioid plexus of the 

 lateral ventricle. This is continuous with that of the third 

 ventricle through the foramen of Monro or interventricular 

 foramen, which connects these ventricles. In front of the 

 foramen, the medial wall is formed by the septum.^ 



Division of the brain in the median plane reveals another 

 instructive view, showing to particular advantage the larger 

 commissures and the relations of the ventricles, besides other 

 features. In addition to the commissures already mentioned, 

 there may be observed the hippocampal commissure, which 

 appears as a thin flat band directly ventral to the posterior 

 part of the corpus callosum with a thickened anterior portion; 

 the anterior commissure, a distinct cylindrical strand crossing 

 in the anterior wall of the third ventricle (the lamina termi- 

 nalis); and the posterior commissure, a less conspicuous 

 structure just below the habenular commissure (PI. I\'., 

 XXVI.). 



iSee p. 93. 



