140 



ANATOMY OF VERTEBRATES. 



they form the ( superior longitudinal commissure/ fig. 122, o ; and 

 fibres are traceable from both extremities to the l perforated space,' 

 figs. 82, 120, x. The dissection, fig. 122, shows also the longitu- 

 dinal fibres extending from the anterior to the inferior and poste- 

 rior lobes, and forming the ( external longitudinal commissure,' c, 

 above which are seen part of the radiating fibres, s, interlacing with 

 those of the corpus callosum, c ; which is overarched by the outer- 

 most of the superior longitudinal commissural fibres, o. Above 



1 23 



Dissection of the left hemisphere of the brain, from the inner side. XXXIII". 



these are shown the fibres which mainly form the convolutions, but 

 which include not only the ' radiating ' fibres, but those of the 

 ' transversely commissural' and 'longitudinally commissural' kinds: 

 they terminate in or blend with the grey matter which forms the 

 outer crust of the hemisphere. In a section of this substance in a 

 recent brain, a white line is seen to separate it into two layers, as 

 in fig. 124. More closely scrutinised, the following strata have 

 been defined from the surface downward : — a thin superficial white 

 layer, a thick reddish grey layer, the intermediate white layer, a 

 thicker grey layer, a third thin white layer, and the deepest grey 

 layer receiving the radiating fibres of the white or medullary cere- 

 bral neurine. 1 



1 In the contemporary Reports of my Hunterian Coarse of Lectures, 1842, the 

 chief conclusions of the comparative anatomy of the superficial grey substance in 



