828 



NEUROLOGY 





part of the cingulate gyms already described; and the slit-like interval between 

 it and the upper surface of the corpus callosum is termed the callosal fissure (Fig. 

 727) . If the hemispheres be sliced off to a level with the upper surface of the corpus 

 callosum, the white substance of that structure will be seen connecting the two 

 hemispheres. The large expanse of medullary matter now exposed, surrounded by 

 the convoluted margin of gray substance, is called the centrum ovale majus. 



The Corpus Callosum (Fig. 733) is the great transverse commissure which unites 

 the cerebral hemispheres and roofs in the lateral ventricles. A good conception 

 of its position and size is obtained by examining a median sagittal section of the 

 brain (Fig. 720), when it is seen to form an arched structure about 10 cm. long. 

 Its anterior end is about 4 cm. from the frontal pole, and its posterior end about 

 6 cm. from the occipital pole of the hemisphere. 



Fid. 733. Corpus callosum from above. 



The anterior end is named the genu, and is bent downward and backward in front 

 of the septum pellucidum; diminishing rapidly in thickness, it is prolonged backward 

 under the name of the rostrum, which is connected below with the lamina terminalis. 

 The anterior cerebral arteries are in contact with the under surface of the rostrum ; 

 they then arch over the front of the genu, and are carried backward above the body 

 of the corpus callosum. 



The posterior end is termed the splenium and constitutes the thickest part of the 

 corpus callosum. It overlaps the tela chorioidea of the third ventricle and the 

 mid-brain, and ends in a thick, convex, free border. A sagittal section of 



