52 



Mr. "W. H. Broadbent on the Structure 



[June 17, 



between different parts of the hemisphere is much more extensive than has 

 hitherto been described, and that the fibres more commonly run longitu- 

 dinally in the convolutions than cross from one to another, while large 

 tracts of convolutions have no direct connexion with the crus, central 

 ganglia, or corpus callosum. 



The preponderance of commissural over radiating fibres is indicated by 

 a comparison of the sectional area of the latter as they issue from the 

 central ganglia with the large surface of white matter displayed in the 

 centrum ovale. The dissection by which this is shown in detail is begun 

 on the uuder surface of the temporo- or occipito-sphenoidal lobe. 



In this lobe the fibres are almost entirely longitudinal in their general 

 direction. From near the apex fibres can be followed backwards in the 

 two or three convolutions on the outer side of the gyrus uncinatus to near 

 the centre of this surface of the lobe, where they end in the grey matter of 

 a sort of lobule which I have ventured to call the collateral lobule. From 

 the collateral lobule other fibres pass to the convolutions at the occipital 

 extremity of the lobe, to convolutions on its outer side and to the calcarine 

 end of the uncinate gyrus. These convolutions, comprising all those of the 

 temporo-sphenoidal lobe except the gyrus uncinatus, the iufra-marginal 

 and parallel gyri, and the continuation of the two latter round the apex 

 receive no fibres whatever from the crus, central ganglia or corpus callosum, 

 but the ant. commissure spreads into them. 



Beneath these is a beautiful plane of fibres which forms the floor of the 

 descending cornu of the lateral ventricle, except at the anterior end ; it 

 forms the floor also of the ventricle at the entrance to the cornu, i. e. in the 

 eminentia accessoria and of the posterior cornu ; but here fibres of the C. 

 callosum are mingled with those of the plane spoken of. This plane is 

 formed as follows : along the axis of the lobe, in the hollow left by the 

 removal of the superficial convolutions, runs a band of fibres from the apex 

 to the posterior extremity ; anteriorly this band contains numerous fibres, 

 but in passing backwards they spread out towards the inner border of the 

 lobe into a continuous lamina, which rests upon the lining membrane of 

 the ventricle and its cornua. Some of the fibres run in the upper wall of 

 the calcarine fissure to the postero-parietal lobule, others form a layer in 

 the lower wall of this fissure, L e. in the calcarine division of the gyrus unci- 

 natus. The G. uncinatus remains as an elevation along the inner side of 

 the shallow valley resulting from the dissection described, little encroached 

 upon by it ; its superficial fibres, however, must be removed to display the 

 plane just mentioned. It incloses the cornu of the ventricle and the hippo- 

 campus, and is thus not a solid mass. Its fibres can be divided into two 

 layers, a superficial set, the general direction of which is from the outer or 

 collateral side anteriorly, backwards and inwards to the grey matter on its 

 flat surface ; and a deeper set, the fibres of which at the anterior part of 

 the gyrus occupy its entire width, in passing backwards they converge, and 

 near the inner border have a twisted arrangement, the inner fibres passing 



