IXTERXAL PARTS. 



539 



length ■u'ith the septum kicidum, a yertical partition between the two 

 lateral ventricles. 



Although it presents a few longitudinal white fibres on its surface, the coi-pus 

 callosum consists almost entirely of fibres having a transverse coui'se towards 

 each side, and spreading in a radiating manner into the substance of the two 

 hemispheres. As the transverse fibres from the anterior and posterior portions of 

 the cerebiTim are necessarily aggregated in large numbers near the corresponding 

 ends of the coii^us callosum, its gi-eater thickness at those points, in comparison 

 with the rest of its extent, is accounted for ; and, since the posterior lobe 

 reaches fui-ther l)eyond the coipus callosum than the anterior, the greater thick- 

 ness behind is also explained. 



Lateral ventricles, or venfriculi iricornes. — By making a longi- 

 tudinal cut through the corpus callosum at a short distance on each 

 side of the middle line, and about midway between the two ends of 

 the hemispheres, an opening is made into the right and left lateral 

 veniricles of the brain (fig. 378). These ventricles form part of the 

 general ventricular space within the cerebrum ; they are serous cavi- 



Fiff. 378. 



I?ig. 378. — Horizontal Sectioit of the Buain showing the Lateral Ventricles and 

 THE Fifth Ventricle opened (from Sapjjey after Vicq-d'Azyr), ^ 



1, the fifth ventricle ; 2, the two laininaj of the septum lucidnm meeting in front of 

 it ; 3, lesser hippocampus of the posterior coruu ; 4, horizontal section of the posterior 

 swelling of the corpus callosum ; 5, middle part of the fornix, where it has been separated 

 from the corpus callosum ; 6, posterior pilhir of the fornix ; 7, hippocampus major 

 descending in the middle cornu ; S, eminentia collateralis ; [i, Literal parts of the fomLx ; 

 10, choroid plexus ; 11, taenia semicircularis ; 12, corpus striatum. 



