690 V7//-: CENTRAL AXIS OF TIIE NERVOUS 8Y8TEX. 



fissure, and receiving in tho middle of its inferior face the insertion of tho 

 cerebral peduncles. 



This mass, seven to nine times more voluminous than tho cerebellum, 

 fills tho anterior compartment of the oramal cavity, and thus occupies the 

 greater portion of that space. 



It exhibits for study its external conformation, its internal conformation, 

 and its structure. 



Fig. 329. 



tff 



ANTERO-POSTERIOU AND VERTICAL SECTION OF THE ENCEPHALON TO ONi: SI I Hi 

 OK TIIE MKIHAN I. INK. 



1, 1, Isthmus of the encephalon ; 2, Medulla oblongata; 3, Pons Varolii ; 4, CVix-ln-al 

 peduncle; 5, 6, Corpora bigemina; 7, Optic thalamus ; 8, Pituitary gland ; !>, 

 Pituitary stem; 10, Optic nerve; 11, Cerebellum; 12, 12, Cerebral hemisphere; 

 13, Ventricle of the hemisphere ; 14, Corpus striatum ; 15, Cornu Ammonis ; !<',, 

 Olfactory lobe; 17, Ventricle of the olfactory lobe. 



EXTERNAL CONFORMATION OP THE CEREBRUM. 



Instead of examining the organ in mass, with regard to its external con- 

 formation, we will first consider the great interlobular (or longitudinal) fissure 

 which divides it lengthways ; and afterwards study its two lateral halves, 

 or cerebral hemispheres, which in reality constitute two symmetrical organs. 



1. The Longitudinal Fissure. 



This fissure exists throughout the vertical and antero- posterior circum- 

 ference of the cerebrum, but docs not everywhere offer the same disposition. 

 On the superior aspect of the organ it is very deep, and when the t\v< 

 hemispheres are separated to discover its extent, we see that it reaches to 

 the upper face of the great commissure the corpus callosum. Behind, it 

 curves between the posterior lobes of the hemispheres, but without corres- 

 ponding directly with the posterior thick rounded margin of the corpus 

 callosum, above which there is a feeble adhesion established between tho 

 two halves of the cerebrum, forming a kind of bridge. But in front it passes 

 to the anterior margin of this commissure, and is prolonged in the interval 

 of the anterior lobes of the hemispheres to reach tho inferior face of tho 



organ 



Examined inferiorly, the interlobular fissure is well defined in front, 



