140 



ANATOMY OF VERTEBRATES. 



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

 fibres are traceable from both extremities to the ( 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 e 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 



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



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

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

 f 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 Course of Lectures, 1842, the 

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



