Suggestions have from time to time been made as to the probable functions of the basal ganglia, but so far none of them appear to have been very satisfactory.

It seems to be generally accepted that the optic thalami are not merely sensory centres for every or any special kind of sensation, but are large association ganglia, and it is the endeavour here to point out from anatomical, pathological, and other reasons the kind of associations with which they are probably concerned, and the very important part they play in the life of all animals possessing them.