852 



THE NERVOUS SYSTEM 



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 channel, 

 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 the hemispheres 

 during their growth and elaboration. Through the two foramina indirectly, the 

 cavities of the two lateral ventricles are in communication with each other. 



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

 convex forwards and extending upwards and medianwards into the frontal lobe. 



FIG. 634. HORIZONTAL DISSECTION OF THE CEREBRAL HEMISPHERES. 



The fornix has been removed to show the relation of the tela chorioidea of the third ventricle 

 to the chorioid plexus of the lateral ventricles. (From a mounted specimen in the Anatomical 

 Department of Trinity College, Dublin.) 



CA UDA TE 

 NUCLEUS 



ANTERIOR 



PILLARS 



OF FOKSIX 



Veins of Galen 



POSTERIOR 



PILL A Rti 



OF FORNIX 



Straight sinus 



CERE- 

 SELL UM 



CORPUS 



CALLOSUM 



( ill -WT/'(/7l) 



SEPTUM 

 PKLLUCI- 

 II UM 



VENTRICLE 



STI.'I.I TER- 

 MINAL /.s 1 

 OF TIIA LA- 

 UUS 



THALA.MUH 



Tela 



chorioidea 

 - (velum inter- 

 POBitum) 



I-'IMISRIA 

 IIIPPOCA M- 

 PUS MAJOR 

 KM1XKXT1A 

 COLLA TKR- 



HIPPO- 



CAMPUS 

 MINOR 



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 boundary 

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

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

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



The body or central portion is more nearly horizontal. It lies within the 

 parietal lobe and extends from the interventricular foramen to the level of the 

 splenium of the corpus callosum. Its roof is formed by the inferior surface of the 

 body of the corpus callosum, and its mesial wall consists of the posterior part of the 

 septum pellucidum, attaching the fornix to the under surface of the corpus callosum. 

 Like the anterior horn, it is given an oblique, ventro-lateral wall by the narrower, 



