THE BRA IX. AXD ITS MEMBRANES. 



755 



already described. It carries with it, in its floor, a prolongation of its corre- 

 sponding half of the for nix, which, consequently, 

 in the adult brain, is described as dividing poste- 

 riorly into its two posterior' pillars. As this lobe 

 curves downward it embraces, but does not adhere to, 

 the pulvinar of the optic thalauius. 



In the foetal brain a wide shallow cleft (Fig. 

 444) lies between the temporal and portions of the 

 frontal and parietal lobes, but this deepens and nar- 

 rows (/?'.>.<;//' "/ Xi/l>'iiis) as the lobe develops. The 

 'ai-ity of the temporal lobe lies close to its inner 

 aspect, the bulk of the lobe developing externally. 

 A portion of the corpus callosum roofs over the 

 beginning of the temporal cavity. 



The Lateral Ventricles, and Structures in Connection therewith. 



The lateral ventricles are the cavities of the hemispheres, each being distinct 

 from the other. In each hemisphere the lateral ventricle is situated in^its lower 

 and inner regions, being surrounded above, in front and externally, by the solid, 

 chiefly white, matter of the hemisphere. Each lateral ventricle* communicates 

 through the foramen of Monro with the third ventricle, and is lined by a thin 

 diaphanous membrane (the ependymd), covered by nucleated epithelium with 

 cilia, scattered here and there in patches. It is moistened by a serous fluid, 

 which is sometimes, even in health, secreted in considerable quantity. Each is 

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



Each lateral ventricle consists (Fig. 445) of a central cavity, or body, 



and three accessory cavities or cor- 

 nua. The anterior cornu curves 

 forward and outward into the sub- 

 stance of the frontal lobe. It com- 

 prises that portion of the ventricle 

 which is anterior to the foramen of 

 Monro. The body comprises that 

 portion of the ventricle which lies 

 between the foramen of Monro and 

 the posterior part of the corpus cal- 

 losum. It is situated low down in 

 the parietal lobe. From its poste- 

 rior extremity diverge the two fol- 

 lowing : The posterior cornu, called 

 the digital cavity, curves backward 

 into the occipital lobe; the middle 

 cornu descends into the temporal 

 lobe. 



If the upper part of both hemi- 

 spheres is removed, about half an 

 inch above the level of the corpus 

 callosum, the internal white matter 

 will be exposed. It is an ' oval- 

 shaped centre, of white substance, 

 surrounded on all sides by a narrow 

 convoluted margin of gray matter, 

 which presents an equal thickness in 

 nearly every part. This white cen- 

 tral mass has been called the centrum 

 ovale minus. Its surface is studded with numerous minute red dots (puncta vascu- 



FIG. -Wo. Right later* 

 (Gegenbaur.) 



seen from above. 



