INTERIOR OF THE CEREBRUM. 



661 



hemisphere, one on either side of the middle line. They are separated from each 

 other by a mesial vertical partition, the septum lucidum, but communicate with 

 the third ventricle and indirectly with each other through the foramen of Monro. 

 They are lined by a thin, diaphanous membrane, the ependyma, which is covered 

 by ciliated epithelium, and are moistened by a serous fluid, which, even in health, 

 may be secreted in considerable amount. Each lateral ventricle consists of a cen- 

 tral cavity or body, and three prolongations from it, termed cornua. The anterior 

 cornu curves forward and outward into the frontal lobe ; the posterior backward 

 and inward into the occipital lobe ; and the middle descends into the temporal 

 lobe. 



The central cavity or body of the lateral ventricle is situated in the lower part 

 of the parietal lobe. It is an irregularly curved cavity, triangular in shape on 



FIG. 354. The lateral ventricles of the brain. 



transverse section, and presents a roof, a floor, and an inner wall. Its roof is 

 formed by the under surface of the corpus callosum ; its inner wall is 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 backward : the caudate 

 nucleus of the corpus striatum, tcenia semicircularis, optic thalamus, choroid plexus, 

 one-half of the fornix and its posterior pillar. 



The anterior cornu passes forward and outward, with a slight inclination down- 

 ward, from the foramen of Monro into the frontal lobe, curving round the anterior 

 extremity of the caudate nucleus. It is bounded above by the corpus callosum. 

 and below by the upper surface of its reflected portion, the rostrum. It is bounded 

 internally by the anterior portion of the septum lucidum, and externally by the 



