874 



THE NERVOUS SYSTEM 



localities the space may be quite appreciable, while in other places the walls may 

 be approximate or even in apposition. Each lateral ventricle is a completely 

 closed cavit}^ except at the interventricular foramen. However, a strip of the 

 floor of the inferior cornu is separated from the exterior of the brain by only the 

 thin, non-nervous lamina forming the floor of the chorioid fissure. 



The interventricular foramen (foramen of Monro), by which the lateral ven- 

 tricle is continuous with the cavity of the third ventricle, is a small, roundish chan- 



FiG. 686. — A Cast of the Four Ventricles of the Encephalon. (After Welcker.) 



Anterior cornu of lateral ventricle 



Interventricular foramen (Monroi) 



Third ventricle 



Inferior cornu of lateral ventricle 



Aqueduct of cerebrum 



Fourth ventricle 

 Posterior cornu of lateral ventricle 



nel, 2 to 4 mm. wide, which opens into the mesial side of the posterior end of the 

 anterior cornu. It is bounded in front by the free portion of the anterior pillars 

 of the fornix, and behind by the anterior tubercle of the thalamus. That the greater 

 part of the lateral ventricle is posterior to it is due to the backward extension of 



Fig. 687. — Diagram of Sagittal Section through Lateral Part of Right Hemisphere 

 SHOWING Lateral Ventricle from the Mesial Side of the Section. 



Chorioid plexus 



Bulb of posterior 

 cornu 



Hippocampus 

 minor 



Corpus callosum 



Septum pellucidum 



Fornix 



Caudate nucleus 



Interventricular foramen 

 Caudate nucleus 



Collateral eminence 



Hippocampus major 

 Chorioid plexus of inferior cornu 



Internal capsule 

 Lenticular nucleus 

 Anterior commissure 



the hemispheres during their growth and elaboration. Through the two foramina 

 indirectly, the cavities of the two lateral ventricles are in communication with 

 each oth(!r. 



The walls of the lateral ventricle. — Tlic anterior cornu is a bowl-like cavity, 

 convex forward and extending downward and medialwartl into the frontal lobe. 

 Above and anteriorly it is bounded by the under surface of the corpus callosum and 

 the radiations of its genu into the substance of the frontal lobe. Its median bound- 

 ary is the septum pellucidum; the head of the caudate nucleus (part of the corpus 

 striatum) gives it a bulging, infero-lateral wall, and the balance of its floor is 

 formed by the white substance of the orbital part of the frontal lobe. 



