330 NEUROLOGY, OR ANATOMY OF NERVOUS SYSTEM 



terior portion; the former lying in the middle fossa of the 

 skull and the posterior lying on the upper surface of the ten- 

 torium cerebelli. 



From before backward the following parts come into view: 

 Longitudinal fissure, corpus callosum, lamina cinerea, olfactory 

 bulb and tract, fissure of Sylvius, anterior perforated space, 

 optic commissure, tuber cinereum, infundibulum, pituitary body, 

 corpora albicantia, posterior perforated space, crura cerebri, pons, 

 medulla, and cerebellum. 



The great longitudinal fissure completely separates the right 

 and left hemispheres, and at the bottom of it is the corpus 

 callosum. 



The corpus callosum is placed nearer the front than the 

 back of the hemispheres, being convex from before backward 

 above, concave below; the fibers run transversely, but along 

 the middle line is a longitudinal raphe with a white band on 

 each side, the mesial longitudinal strice, and near the margin 

 some lateral longitudinal stria*. 



The lamina cinerea is a thin layer of gray matter lying be- 

 tween the chiasma and the corpus callosum, and continuous 

 with the gray matter of the anterior perforated space on each 

 side. It forms part of the floor and anterior boundary of the 

 third ventricle. 



The olfactory tract runs in a groove close to the great longi- 

 tudinal fissure on the under surface of the frontal, and ends 

 in an enlargement, the bulb, from which the olfactory nerve 

 descends through the cribriform plate. Behind, the tract 

 divides into two roots. The outer runs back along the margin 

 of the anterior perforated space to the Sylvian fissure; the 

 inner to the longitudinal fissure. The triangular space between 

 the two roots is occupied by gray matter forming part of the 

 tuber olfactorium, which lies in a depression on the frontal lobe, 

 and is composed internally of white matter. 



The fissure of Sylvius lodges the middle cerebral artery. 

 At its inner part is the fasciculus unciformis, connecting the 

 frontal and temporal lobes. 



The anterior perforated space is a triangular depression at 

 the inner side of the Sylvian fissure, of a grayish color, and is 

 pierced by many small vessels passing to the corpus striatum, 

 under which it lies. 



The optic commissure, or chiasma (see Optic Nerve), is formed 



