THE BRAIN AND ITS MEMBRANES. 



757 



lobe, where they meet the outer olfactory roots. They are called the peduncles 

 A' the corpus callosum. Posteriorly, the corpus callosum forms a thick rounded 

 fold, called the splenium or pad, which is free for a little distance as it curves 

 forward, and is then continuous with the fornix below. On its upper surface 

 the structure of the corpus callosum is very apparent, being collected into coarse 

 transverse bundles. Along the middle line is a linear depression, the raplie, 

 bounded laterally by two or more slightly elevated longitudinal bands, called the 



w . w O / 



stria longitudinales or nerves of Lancisi ; and, still more externally, other longi- 

 tudinal stride are seen beneath the convolutions which rest on the corpus callo- 

 sum. These are the strife longitudinales laterales or tcenice tectce. The under 

 surface of the corpus callosum is continuous behind with the fornix, being sepa- 

 rated from it in front by the septum lucidum, which forms a vertical partition 

 between the two ventricles. On each side the fibres of the corpus callosum 

 extend into the substance of the hemispheres, connecting them together. The 

 greater thickness of the two extremities of this commissure is explained by the 

 fact that the fibres from the anterior and posterior parts of each hemisphere do 

 not pass directly across, but take a curved direction. The peduncles of the cor- 

 pus callosurn may be traced upward around the genu to become continuous with 

 the strice longitudinales, or nerves of Lancisi, on the upper surface of the corpus 

 callosum. 



The fibres from the splenium, which curve backward to roof in the poste- 

 rior cornu are known as the forceps major ; those from just above the genu. 

 which curve forward to roof in the front part of the anterior cornu constitute 



Nucleus 

 eaudatus\ 



Corpus 



M0M 



Will'/' 



FIG. 447. Transverse vertical section of the brain, X . anterior to the middle commissure; the cut surface 

 s forward. 1. putamen. 2 and 3. globus pallidus. (Gegenbaur.) 



the forceps minor ; while the term tapetum is given to the main body of the 

 fibres. 



The central cavity, or body, of the lateral ventricle is comparatively wide, but 

 is a mere slit as regards its perpendicular diameter. It is (Fig. 447) bounded, 

 above, by the under surface of the corpus callosum, which forms the roof of the 

 cavity. Internally i.< a vertical partition, the posterior portion of the septum 

 lucid mn, which separates it from the opposite ventricle, and connects the under 

 surface of the corpus callosum with the fornix. Its floor is formed by the fol- 

 lowing parts, enumerated in their order of position from without inward : the 



