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Proceedings of Boy cd Society of Edinburgh. [jan. 31 , 
1. Foville long ago (“ Traite complet de l’Anatomie, de la Physio- 
logic, et de la Pathologie du Systeme Nerveux Cerebro-spinal,” Atlas) 
showed that an arched ridge of fibres could be exposed by simple 
dissection turning downwards at each side of the corpus callosum, 
and figured appearances which, allowing for a certain amount 
of artistic embellishment, substantially represent what actually 
exists. (The author here exhibited a brain, previously hardened 
in Muller’s fluid, in which this dissection had been made, and in 
which the arcuate mass of fibres was distinctly displayed. He 
further showed this arcuate mass in horizontal sections prepared by 
his gelatine-potash method, in which it was quite clearly mapped out. 
Its fibres had a more or less transverse direction, so that they con- 
trasted with those coming from the cortex, and the outer border of 
the mass where they turn downwards was quite sharply differentiated. 
The fact that the arcuate mass is seen on horizontal section com- 
pletely does away with the notion that Foville’s dissection was 
artificial. In a series of horizontal sections the crest of the ridge 
was found to correspond in position with that in the dissection, the 
site of it being at a point considerably below the level of the cortex 
at the vertex.) 
2. That the crossed callosal tract is co-extensive with the corpus 
callosum can be proved by dissecting it out, or by examining it in a 
horizontal gelatine-potash preparation. 
3. To trace microscopically the fibres curving downwards from 
the corpus callosum is not such an easy matter as might be supposed, 
owing in great part to the fibres running in different planes between 
their points of origin and insertion. 
Meynert has alleged that he could trace single fibres from the 
cortex of one side through the corpus callosum into the cortex of 
the opposite. For my own part I can hardly credit this statement, 
for, after having spent an immense deal of labour upon the subject, 
and working with methods far more refined than those employed by 
Meynert, it has never been my good fortune to follow a single axis 
cylinder from the one side to the other even in the smallest 
mammals. The fibres diverge and run so obliquely after crossing 
that I question if a section made in any one plane would suffice to 
expose their entire course. 
If the brain be cut perpendicularly in an oblique antero-posterior 
