DISSECTION OF THE BRAIN, OR ENCEPHALON. 



255 



genu, and the reflected portion the rostrum. The rostrum becomes 

 narrower as it descends, and is connected to the optic commissure 

 by the lamina cinerea. Along the middle line of its lower face the 

 corpus callosum is connected posteriorly with the fornix, and 

 anteriorly with the septum lucidum ; and on each side it forms the 

 roof of a cavity in the hemisphere — the lateral ventricle. Nearly all 

 the fibres of the corpus callosum have a transverse direction ; but 

 on each side of the longitudinal middle line of its upper face there 

 are a few longitudinal fibres termed the striae longitudinales, or nerves 

 of Lancisi. 



Directions. — If the corpus callosum be now cut through in the 

 longitudinal direction, a little to one side of the middle line, and 



Fig. 35. 

 Corpus Callosum and Inner Face ok the Cerebral Hemisphere. 

 1, 2. Right and left cerebral hemispheres ; 3. Cerebellum ; C. Corpus callosum ; G. F. Gyrus 

 fornicatus (its callosal portion) ; C. M. Calloso-marginal fissure ; A. M. Antero-marginal convolu- 

 tion ; P. M. Postero-marginal convolution. 



dissected outwards, the lateral ventricle will be exposed. The corpus 

 callosum, it will now be seen, is thickest at its posterior extremity, 

 and thinnest at its middle. 



The Lateral Ventricles (Plate 35) are two in number, one in each 

 hemisphere. They are separated from one another along the middle 

 line by the fornix and septum lucidum, but beneath the former body 

 they communicate through the foramen of Monro. The central portion 

 of each cavity is termed the body, and its prolongations before and 

 behind are termed respectively the anterior and the descending cornu. 



On the floor of the body of the cavity the following objects will 

 be noticed : In front, a large pear-shaped grey eminence — the corpus 



