THE CEREBRAL HEMISPHERES 



937 



The Lateral Ventricles. An incision through the corpus callosum, on either side 

 of the median plane, will expose two large, irregular, symmetrically situated 

 cavities, the lateral ventricles (paraceles), extending through a great part of each 

 cerebral hemisphere. Each lateral ventricle communicates with the third ven- 

 triflp through a small opening, the foramen of Monro, situated between the forni- 

 column (anterior pillar of fornix) and frontal end of thalamus. The cavity is 

 lined throughout by ependyma; it is narrow in some and wide in other localities, 

 and contains cerebrospinal fluid. 



The shape of the ventricle is best understood by reference to a cast of its 

 interior, and its location within the cerebrum may be appreciated by a study of 

 Figs. 689 and 090. Conventionally the lateral ventricle or paracele is described as 

 being composed of a body or cella and three horn-like extensions or cornua. Viewed 

 laterally its contour corresponds to that of the cerebral hemisphere and its cornua 

 project toward the three poles viz., frontal, occipital, and temporal. 



FIG. 689. Showing the ventricular system of the brain as a solid east as if seen through a transparent brain. 



The body (pars centralis ventriculi lateralis) or cella of the lateral ventricle is 

 defined as that portion which extends from the foramen of Monro to the region 

 of the splenium. Its frontal prolongation is called the anterior horn or precornu. 

 Near the splenium the cavity may be traced ventrolaterad into a capacious part 

 (trigonum ventriculi^), from which the posterior horn (postcornu) and middle horn 

 (medicornu) are prolonged, respectively, toward the occipital and temporal poles. 



The anterior horn or precornu (cornu anterius} passes frontad, inclined slightly 

 ventrolaterad. Its floor is the head (capuf) of the caudate nucleus, forming a 

 rounded incline sloping mesad toward a trench-like recess floored by the rostrum 

 of the corpus callosum. Its roof is the anterior forceps of the corpus callosum. 

 Its mesal wall is formed by a portion of the hemiseptum of the septum lucidmn. 

 Laterally it is limited by the apposition, at an acute angle, of corpus callosum 

 and caudate nucleus. Its apex reaches the ventricular surface of the genii of 



