364 NERVOUS SYSTEM. 
each side it passes laterad, forming the roof of the lateral 
ventricle. Its cranial part lies dorsad of the corpus striatum, 
and its caudal part dorsad of the thalamus. _Laterally its fibres 
radiate into the substance of the hemispheres. At its cranial 
end the corpus callosum bends ventrad and then caudad (Fig. 
143). The part which turns to pass ventrad is the genu (Fig. 
143, g) or knee, while the part which projects caudad is the 
rostrum (7). The caudal border of the corpus callosum is also 
thickened and turned ventrad and is called the splenium (Fig. 
143, 5); it lies dorsad of the cranial corpora quadrigemina (2). 
Fic. 148.—Fornix, HiprpocaMpus, AND Corpus STRIATUM. 
The dorsal portion of the hemispheres has been dissected away and the corpus 
callosum removed. a, fornix; 4, columns or pillars of the fornix; ¢, crura of the 
fornix; @, hippocampus; ¢, choroid plexus of the lateral ventricles overlying the fim- 
bria (the choroid plexus shows an artery), /, corpus striatum; g, corpora quadri- 
gemina; %, position of the interventricular foramen (foramen of Monroe). 
The caudal half of the ventral surface of the corpus callosum 
is united with the fornix (Fig. 143, 7). 
The fornix (Fig. 148, a; Fig. 143, w, v; Figs. 150-152, 4) 
consists of an arched tract of longitudinal fibres near the medial 
border of each hemisphere, ventrad of the corpus callosum. 
Each tract begins in the mammillary bodies, and passes dorsad, 
the two converging until they run side by side, forming a 
cylindrical dorsoventral bundle known as the columns or pillars 
