]28 



THE LATERAL VENTRICLES. 



bend named the genu (fig. 91). The inferior or reflected portion, which is named 

 the rostrum, becomes gradually narrower as it descends, and is connected with the 

 lamina cinerea by a thin white layer, the commissura baseos alba of Henle. It gives 

 off also two bands of white substance, the peduncles of the corpus callosum, which, 

 diverging from one another, run backwards across the posterior margin of the 

 anterior perforated space on each side to the tip of the temporal lobe, where they 

 meet the inner olfactory roots. These peduncles traced upwards around the genu 

 are found to be continued into the mesial longitudinal striae. 



Behind, the corpus callosum terminates in a free thickened border, named the 

 splenium, but this term is sometimes restricted to the under part of this thickened 

 border, which appears as if rolled round under the rest (splenium proper, Beevor). 



Fig. 92. VIEW OF THE CORPUS CALLOSUM FROM ABOVE (from Sappey after Foville). J 



The upper surface of the corpus callosum has been fully exposed by separating the cerebral hemi- 

 spheres and throwing them to the side ; the gyrus fornicatus has been partly detached, and the trans- 

 verse fibres of the corpus callosum traced for some distance into the cerebral medullary substance. 



1, the upper surface of the corpus callosum ; 2, median furrow or raphe ; 3, longitudinal strise 

 bounding the furrow ; 4, swelling formed by the transverse bands as they pass into the cerebrum, 

 arching over the side of the lateral ventricle ; 5, anterior extremity or knee of the corpus callosum ; 6, 

 posterior extremity ; 7, anterior, and 8, posterior fibres proceeding from the corpus callosum into the 

 frontal and occipital lobes respectively ; 9, margin of the swelling ; 10, anterior part of the gyrus 

 fornicatus ; 11, fissure between the corpus callosum and this convolution opened out ; outside 12, is the 

 termination of the calloso-marginal fissure, and before 13 is the parieto-occipital fissure ; 13, upper 

 surface of the cerebellum. 



The mesial part of the under surface of the corpus callosum is connected behind 

 with the fornix, and in the rest of its length with the septum lucidum, a vertical 

 partition between the two lateral ventricles, which is included in the anterior bend 

 of the corpus callosum. On the sides the corpus callosum roofs in the body and 

 anterior horn of the lateral ventricles. The enlarged posterior part or splenium lies 

 over the mesencephalon, with pia mater between. The transverse fibres of the 

 corpus callosum pass in a radiating manner, interlacing with those of the internal 

 capsule, through the medullary centre to the cortex of each hemisphere. Those in 

 front which sweep round into the prefrontal region form the so-called forceps minor. 



