542 



THE CEREBRUM. 



where it is nearly half an inch. It is arched from before backwards. Its 

 upper surface is distinctly marked by transverse furrows, which indicate 

 the direction of the greater number of its fibres. It is also marked in the 

 middle by a slight longitudinal groove, the raphe, which is bounded laterally 

 by two white tracts, placed close to each other, named striae longitudinales, 

 or nerves of Lancisi. On each side, near the margin, are seen other 

 longitudinal lines (striae longituclinales laterales) occasioned by a few scanty 

 white fibres. 



In front, the corpus callosum is reflected downwards and backwards, 

 between the anterior lobes, forming a bend named the genu. The inferior 

 or reflected portion, which is named the rostrum, becomes gradually nar- 

 rower as it descends, and is connected by means of the lamina cinerea with 

 the optic commissure. It also gives off the two bands of white substance, 

 already noticed as the peduncles of the corpus callosum, which, diverging 

 from one another, run backwards across the anterior perforated space on 

 each side to the entrance of the Sylvian fissure. 



Fig. 371. 



semicircularis ; y, enrinentia collaterals. 



Fig. 371. THE LATERAL 

 VENTRICLES OPENED BY 

 A HORIZONTAL SECTION, 

 AND THE MIDDLE CORNU 

 EXPOSED ON THE RIGHT 



SIDE. 



a, b, anterior and pos- 

 terior parts of the great 

 longitudinal fissure ; c, 

 section of the anterior part 

 of the corpus callosum ; d, 

 posterior part of the same ; 

 e, the left choroid plexus ; 

 /, the fornix ; g, the an- 

 terior; 7t, the posterior, 

 and q, the descending 

 cornu of the lateral ven- 

 tricle ; k, Jc, corpora 

 striata ; I, I, optic tha- 

 larai ; n, n, right and left 

 hippocampus minor ; o, 

 posterior pillar of the for- 

 nix ; v, the corpus fimbri- 

 atura into which it passes; 

 <?, cornu ammonis or pes 

 hippocampi ; A, the medul- 

 lary substance of the cere- 

 bral hemisphere ; r, part 

 of the cortical substance 

 showing alternate grey and 

 white matter ; s, s, tsenia 



Behind, the corpus callosum terminates in a free thickened border (bour- 

 relet, pad), the under surface of which is also free for a short distance 

 forwards. 



The under surface of the corpus callosum is connected behind with the 

 fornix, a structure to be presently described, and in the rest of its length 

 with the septum lucidum, a vertical partition between the two lateral ven- 

 tricles. 



