Franz Joseph Gall (9 March 1758 – 22 August 1828): neuroanatomist, physiologist, and pioneer in the study of the localization of mental functions in the brain (http://en.wikipedia.org/wiki/Franz_Joseph_Gall)

Legitimate discoveries

1) cortex as functioning tissue, not just protective covering ("cortex" is literally "bark" or "skin")

2) commissures (or connecting pathways) between brain hemispheres, other than the already known corpus callosum

3) crossing of ascending nerve pathways from spinal cord to contralateral hemispheres of the brain

4) distribution of and distinction between grey matter and white matter tracts (where grey matter was recognized in the 20th century as mostly neuron cell bodies doing information processing, and white matter as mostly myelinated axons sending signals over longer distances)

Phrenology

As originally put forward, there were four cardinal premises [of phrenology], namely that:

(1) the brain is the material instrument through which the mind holds intercourse with the outer world;

(2) the mind entails a congeries [or jumbled collection] of discrete mental faculties each with its own specific center or organ;

(3) the size of each organ corresponds with the functional efficiency of each faculty; and

(4) the development of the organ is reflected in the shape, size and irregularities of the encompassing cranium.

from MacDonald Critchley (1979) The Divine Banquet of the Brain, New York, Raven Press. cited in: Jerry Fodor (1983) Modularity of Mind: An Essay on Faculty Psychology. Cambridge, Mass.: MIT Press. pp. 131-132 (from Fodor (1983) footnote [10] quoting Critchley)

So, why isn't Gall honored in the textbooks? The story of Gall's posthumous reputation is a sad illustration of the maxim that the good men do is oft interred with their doctoral dissertations. Gall made two big mistakes, and they finished him: he believed that the degree of development of a mental organ can be measured by the relative size of the corresponding brain area, and he believed that the skull fits the brain "as a glove fits a hand." Phrenology followed as the night the day, and with it all sorts of fraud and quackery, for none of which Gall was responsible but for much of which he appears to have been retrospectively blamed. It is lucky for us that we don't make mistakes any longer; those who do so clearly have little to expect from history or from the intellectual charity of their professional colleagues.

from Jerry Fodor (1983) Modularity of Mind: An Essay on Faculty Psychology. Cambridge, Mass.: MIT Press. pp. 22-23

More information on phrenology:

http://www.historyofphrenology.org.uk/overview.htm