The vertebrate brain can be subdivided as follows:
In most vertebrates the metencephalon is the highest integration center in the brain, whereas in mammals this role has been adopted by the telencephalon. Therefore the cerebrum is the largest section of the mammalian brain and its surface has many deep fissures (sulci) and grooves (gyri), giving an excessively wrinkled appearance to the brain.
See cephalic disorders for information on congenital development disorders relating to the brain.
The adult human brain usually weighs about 1 - 1.5 kilograms in an average volume of 1,600 cubic centimetres. The intelligence of the individual is not necessarily related with the weight of the brain, but with the efficiency and number of connections between cells.
The blood supply to the brain involves several arteries that enter the brain and communicate in a circle called the circle of Willis. Blood is then drained from the brain through a network of sinuses that drain into the right and left internal jugular veins.
During many past millennia, the function of the brain was unknown. Ancient Egyptians threw the brain away prior to the process of mummification. Ancient thinkers such as Aristotle imagined that mental activity took place in the heart. The Alexandrian biologists Herophilus and Erasistratus were among the first to conclude that the brain was the seat of intelligence. Galen's theory that the brain's cavities, or ventricles, were the sites of thought and emotion prevailed until the work of the Renassiance anatomist Vesalius.