522 NERYOUS SYSTEM. 



bundles of white substance, which, diverging from one another, pass backwards, 

 across the anterior perforated space, to the entrance of the fissure of Sylvius. 

 They are called the peduncles of the corpus callosum. Posteriorly, the corpus 

 callosum forms a thick, rounded fold, which is free for a little distance, as it 

 curves forwards, and is then continuous with the fornix. On its upper surface, 

 its fibrous structure is very apparent to the naked eye, being collected into coarse, 

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

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

 longitudinales or nerves of Lancisi ; and, still more externally, other longitudinal 

 stria? are seen, beneath the convolutions, which rest on the corpus callosum. These 

 are the striae longitudinales laterales. The under surface of the corpus callosum 



Fig. 267. The Lateral Ventricles of the Brain. 



is continuous behind with the fornix, being separated from it in front by the 

 septum lucidum, which forms a vertical partition between the two ventricles. On 

 either side, the fibres of the corpus callosum penetrate into the substance of the 

 hemispheres, and connect together the anterior, middle, and part of the posterior 

 lobes. It is the large number of fibres derived from the anterior and posterior 

 lobes, which explains the great thickness of the two extremities of this commissure. 



An incision should now be made through the corpus callosum, on either side of the raphe, 

 when two large irregular cavities will be exposed, which extend throughout the entire length of 

 each hemisphere. These are the lateral ventricles. 



The lateral ventricles are serous cavities, formed by the upper part of the 

 general ventricular space in the interior of the brain. They are lined by a thin 

 diaphanous lining membrane, covered with ciliated epithelium, and moistened by a 



