The two hemispheres that make up 85% of the brain's weight are collectively known as the

The proper word that needs to be supplied or filled in the blank is CEREBRUM. This makes up a good 85% of the entire weight of the brain. For most vertebrates, this is the most anterior part of the brain, separated into two hemispheres, the left and the right. 

This is also comprised of several other parts such as the subcortical structures which consists of basal ganglia, hippocampus, olfactory bulb among others. The cerebrum functions to control the emotions, personality, vision, hearing, and much more.