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NERVOUS SYSTEM. 



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-shaped cavities will be exposed, which extend through a great part of the 

 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 



Fig. 331. The Lateral Ventricles of the Brain. 



by a serous fluid, which is sometimes, even in health, secreted in considerable 

 quantity. These cavities are two in number, one in each hemisphere, and they 

 are separated from each other by a vertical septum, the septum lucidum. 



Each lateral ventricle consists of a central cavity, or body, and three smaller 

 cavities or cornua, which extend from it in different directions. The anterior 

 cornu curves forwards and outwards, into the substance of the anterior lobe. 

 The posterior cornu, called the digital cavity, curves backwards into the posterior 

 lobe. The middle cornu descends into the middle lobe. 



The central cavity, or body of the lateral ventricle, is triangular in form. It 

 is bounded, above, by the under surface of the corpus callosum, which forms 

 the roof of the cavity. Internally, is a vertical partition, the septum lucidum, 

 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 following 

 parts, enumerated in their order of position, from before backwards : the corpus 



