540 



THE CEUEBRUM. 



ties, and are lined by a delicate epitheliated strnctnro, the ependyma 

 vcntrkidorum, Avhich, at certain parts in the adult, and probably 

 throughout its whole extent in the foetus, is provided with cilia. In 

 the natural state the walls of the ventricles are moistened internally 

 witli a serous fluid, which sometimes exists in considerable quantity, 

 even in a healthy brain. 



It was formerly a subject of dispute whether the lining of the ventricles 

 consisted of epithelium onlj^ or also of a membrane. It is now recognised 

 that a peculiar form of connective tissue is found throughout the substance 

 of the brain, similar to that whicli has been described in the spinal cord, and 

 like it called neuroglia. A layer of this substance, unmixed with nerve- 

 tissues, but in direct continuitj' with the interstitial web, and not a distinct mem- 

 brane, supports the epithelium. 



The form of the epithelial cells appears to vary in different parts ; these cells 

 being, according to KoUiker. of the flat pavement kind in the third ventricle, 

 and more spherical in_ the lateral ventricles : and, according to Gerlach, cylin- 

 drical in the aqueductus Sylvii. 



From the central part or body of each lateral ventricle the cavity 

 is extended forwards, backwards, and downwards, thus forming an 

 anterior, ajwsferior, and a 7nid(Ue or descendimj comu (fig. 371). 



white matter ; s, s, t 



^'S- 379. pif,_ 379.— The Lateral 



Yenteicles opened by 

 A Horizontal Section, 

 ANi> THE Middle Cornu 



EXPOSED ON THE RIGHT 

 SIDE. -^- 



o, h, anterior and pos- 

 terior parts of the gi-eat 

 longitudinal fissure ; c, 

 section of the anterior jiart 

 of the corpus callosum ; d, 

 posterior part of the same ; 

 c, tlie left choroid plexus ; 

 /, the fornix ; g, the an- 

 terior ; Ii, the posterior, 

 and 0, the descending 

 cornu of the lateral ven- 

 tricle ; 7c, k, corpora 

 striata ; I, I. optic tha- 

 lami ; n, n, right and left 

 hippocampus minor ; o, 

 posterior pillar of the for- 

 nix ; v, the corpus fimbri- 

 atum into which it passes ; 

 ([, cornu ammonis or pes 

 hippocamiii ; h, the medid- 

 lai-y substance of the cere- 

 bral hemisphere ; r, yaxt 

 of the cortical substance 

 showing alternate grey and 

 ;enia semicircularis ; y, emiueutia collatcraiis. 



The lodij of each lateral ventricle is roofed by the corpus callosum, 

 and is separated from its fellow by a vertical partition, the sejifimi 

 Ivcidum (tig. 378, 2), which descends from the corpus callosum to 

 the fornix. In the floor of the ventricle there is seen behind one half 



