Source : Webster's Revised Unabridged Dictionary (1913)

Phrenology \Phre*nol"o*gy\, n. [Gr. ?, ?, the mind + -logy: cf.
   F. phr['e]nologie.]
   1. The science of the special functions of the several parts
      of the brain, or of the supposed connection between the
      various faculties of the mind and particular organs in the
      brain.

   2. 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.

Source : WordNet®

phrenology
     n : a now abandoned study of the shape of skull as indicative of
         the strengths of different faculties