528 Proceedings of Royal Society of Edinburgh. [jan. 31 , 
a meeting-point for many of the callosal fibres before they proceed 
to cross, the individual fibres losing their identity within it by 
splitting into an anastomising common network, from which again 
fresh fibres appear to arise and travel across the corpus callosum 
to the opposite side. 
The fibres which enter this body are chiefly derived from the 
motor centres which in Man have been found to preside over the 
muscles of the tongue and face, that is to say, the lower parts 
of the ascending frontal and parietal convolutions, and it is 
conceivable that the function of the plexus contained in it is to 
correlate and associate their action. 
Destinations of the Callosal Fibres . — After passing into the inner 
and outer capsules, the arched callosal fibres just described become 
united into dense bundles. A very large proportion of them lose 
themselves in the thalamus opticus. The excessively fibrous appear- 
ance which the thalamus presents is due to these fibres passing 
into it. They probably break up into a network, in the meshes 
of which the nerve cells are intercalated. 
Are these nerve cells directly connected with the nerve fibres 
entering the ganglion, or is the network referred to intermediate ? 
It seems more likely that the union is not direct, but that a plexus 
intervenes between the two, and that this plexus simply surrounds 
the nerve cells. I am even not at all convinced that the processes 
of the nerve cells are in all cases directly connected with the plexus. 
May not nerve energy generated in cells exert its influence upon 
nerve fibres in ways other than by direct continuity ? Is it not 
possible that it may be transferred to the coils of a dense plexus 
through the liquid and neuroglia which fill up the intervals in the 
tissue, and that, conversely, peripheral stimuli may thus be eonveyed 
to a nerve cell ? I think this is at least conceivable, and the idea 
has of late been entertained by several physiologists, both in this 
country and abroad. 
Few, if any, callosal fibres end in the caudate nucleus , and, 
curiously, as if supporting this observation, the plexus in this gan- 
glion seems to be very scanty. .The lenticidar nucleus may receive 
through the striae medullares a considerable number, and probably 
some of the fibres connected with the red nucleus may be also 
callosal. A large number appear to end in the pons and medulla 
