690 TEE CENTRAL AXIS OF THE NEBVOUS SYSTEM. 



fissure, and receiving in the miclclle of its inferior face the insertion of the 



cerebral peduncles. . , , ,, 



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



fills the anterior compartment of the cranial cavity, and thus occupies the 



a-reater portion of that space. .^ . , , . ,- 



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



and its structure. 



Fig. 329 



9^ 



ANTEEO-POSTEEIOR AND VERTICAL SECTION OF THE ENCEPHALON TO ONE SIDE 

 OF THE MEDIAN LINE. 



1, 1, Isthmus of the encephalon ; 2, Medulla oblongata ; 3, Pons Varolii ; 4, Cerebral 

 peduncle ; 5, 6, Corpora bigemina ; 7, Optic thalamus ; 8, Pituitary gland ; 9, 

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

 13, Ventricle of the hemisphere ; 14, Corpus striatum • 15, Cornu Ammonis ; 16, 

 Olfactory lobe ; 17, Ventricle of the olfactory lobe. 



BXTEENAL CONFORM &.TION OF 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 cerehral heinispheres, which in reality constitute two symmetrical organs. 



1. The Longitudinal Fissure. 



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

 ference of the cerebrhm, but does not everywhere offer the same disposition. 

 On the superior aspect of the organ it is very deep, and when the two 

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

 the upper face of the great commissure — the corpus oallosum. 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 the 

 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 the inferior face of the 

 organ. 



Examined inferior ly, the interlobular fissure is well defined in front, 



