1869.] 



of the Cerebral Hemispheres. 



55 



the same convolutions ; the corner of the orbital lobule in fact is carried 

 away entirely by the fibres from the fasciculus and island. In the same 

 way fibres starting in the remaining convolutions of the island cross the 

 fissure and turn up in the supramarginal gyrus, leaving the outer surface of 

 the C. striatum perfectly smooth, and converting the Sylvian fissure into a 

 deep wide valley. The wall of the C. striatum thus exposed consists of a 

 lamina of fibres, which radiate in all directions from a small patch of grey 

 matter laid bare at the middle and highest point of the eminence this 

 ganglion forms as seen from this aspect ; and it is possible that there may 

 be here some sort of continuity or connexion between the grey matter of the 

 C. striatum and the overlying part of the convolutions of the island. 

 Except at this point, the convolutions are separated from the C. striatum 

 by a very distinct plane of fibres. 



The gyri operti are thus connected mainly with the supramarginal 

 gyrus and its continuation along the anterior wall of the fissure. Some 

 fibres, however, pass from the grey matter of the overhanging inframarginal 

 gyrus near the apex into the corresponding part of the island, and about 

 the grey nucleus exposed at the summit of the C. striatum deep fibres from 

 the posterior extremity of the hemisphere and from the F. uncinatus seem 

 to join both the nucleus and the overlying grey matter of the island. 



The temporo-sphenoidal lobe having been gradually removed, and with 

 it a great part of the occipital lobe, a stage of the dissection is reached at 

 which the distribution of the fibres of the splenium C. callosi and the rela- 

 tions of the cms and central ganglia, as seen from the under aspect, may 

 be conveniently described. 



On the inferior surface of the posterior extremity of the C. callosum is 

 seen a transverse flattened elevation, which may be compared to the 

 rostrum at the anterior extremity on a smaller scale and adherent to the 

 body of the great commissure. It would thus be looked upon as a re- 

 curved part of the C. callosum. In the middle line it is adherent, but the 

 fibres it sends transversely outwards leave the C. callosum proper, and 

 bend downwards so as to cross the floor of the ventricle instead of the roof ; 

 they pass to the hippocampus major and minor, which they contribute to 

 form, and run across the eminentia accessoria, and along the floor of the 

 posterior cornu. 



The hippocampus minor is formed by the projection into the posterior 

 cornu of the bottom of the calcarine fissure ; but an incision through the 

 bottom of the fissure into the cornu would not split up the hippocampus, 

 but would leave it attached entire to the upper wall of the cornu. The 

 fibres from the splenium, which contribute to the formation of the hippo- 

 campus minor, run longitudinally along it immediately beneath the lining 

 membrane of the ventricle, and when reached by dissection from without 

 present a delicate lamina in the form of a groove between two curved 

 tracts passing backwards to the posterior extremity of the hemisphere, 

 the upper from the C. callosum proper, the lower from its recurved 

 process. 



