What does "phrenology" mean?

Phrenology: In popular usage, the physiological hypothesis of Gall, that the mental faculties, and traits of character, are shown on the surface of the head or skull; craniology. Note: Gall marked out on his model of the head the places of twenty- six organs, as round inclosures with vacant interspaces. Spurzheim and Combe divided the whole scalp into oblong and conterminous patches. Encyc. Brit.