TEE CEREBHUM. 



Inteenal Conformation of the Brain. 



In separating the cerebral hemispheres by their upper face, we discover the 

 great commissure known as the corpus callosum — the first object that presents 

 itself for study in the internal conformation of the brain. 



If we afterwards remove, with a sharp instrument, and by a horizontal 

 section, all that portion of the hemispheres which covers this commissure, and 

 also if the latter be excised to a certain extent to the right and left of the middle 

 line, we shall penetrate two symmetrically disposed cavities in the centre of each 

 hemisphere. These cavities are the lateral or cerebral ventricles. 



They are separated on the middle plane by a thin partition — the septum 

 lucidum — which is attached to the corpus callosum by its upper border, and 

 fixed by its inferior border into the fornix^ a kind of middle arch, beneath which 

 is the foramen of Monro, or orifice communicating with the two ventricles. On 

 the floor of these cavities is observed two large eminences— the corpus striatum 



Fig. 434. 



Fig. 435. 



THE CORPUS CALLOSUM OF THE HORSE, AFTER 

 REMOVAL OP THE UPPER POKTIOM OP THE 

 CEREBRAL HEMISPHERES. 



I, Centrum ovale of Vicq-d'Azyr ; 2, 2, trans- 

 verse fibres of the corpus callosum ; 3, 3, 

 tractus longitudinales; 4,4, cornua, or angles 

 of the posterior extremity ; 5, 5, ditto of 

 anterior extremity. 



ANTERIOR PORTION OF THE LATERAL VENTRI- 

 CLES OF THE DOG, EXPOSED BY REMOVAL OF 

 THE ROOF. 



1, Corpus callosum; 2, anterior part of the 

 corpus callosum, turned forward after de- 

 stroying the septum lucidum, to show the 

 fornix, 3, 3 ; 4, 4, hippocampi ; 5, 5, taeniae 

 semicircularis ; 6, 6, choroid plexus ; 7, 7, 

 corpora striata. 



and the hippocampus ; with a vascular and apparently granular cord forming the 

 cerebral choroid plexus — a dependency of the velum interpositum. 



It now remains to enter into some detail with regard to the anatomical 

 characteristics of all these parts. 



1. The Corpus Callosum (Figs. 434, 435). 



The corpus callosum is a kind of arch thrown over the two lateral ventricles, 

 while at the same time it is a commissure uniting the two hemispheres. It 

 belongs exclusively to Mammalia. 



Composed entirely of white substance, this arch is of an elongated, quadri- 

 lateral sliape, being elongated in an antero-posterior direction ; it thus presents 

 for study two faces, two boi-ders, and two extremities. 



