Human Brain. Computer-enhanced historical artwork of the human brain. The bottom of the brain is seen here with the forebrain at top of image. At centre a cross represents the branching arteries at the base of the brain. This is where the carotid artery, which supplies blood to the head, initially divides. Below this, the pons & brain- stem control vital functions such as breathing. The large, folded cerebrum makes up 70% of the brain and is where conscious thought takes place. At bottom is the cerebellum, which coordinates muscle action & posture. The brain receives about 20% of the heart's output of blood. Drawing by the Italian anatomist Paolo Mascagni (1755-1815).