Franz Joseph Gall on hemispheric symmetries.

Franz Joseph Gall believed that the two cerebral hemispheres are anatomically and functionally similar, so much so that one could substitute for the other following unilateral injuries. He presented this belief during the 1790s in his early public lectures in Vienna, when traveling through Europe between 1805 and 1807, and in the two sets of books he published after settling in France. Gall seemed to derive his ideas about laterality independently of French anatomist Marie François Xavier Bichat (1771-1802), who formulated his "law of symmetry" at about the same time. He would, however, later cite Bichat, whose ideas about mental derangement were different from his own and who also attempted to explain handedness, a subject on which Gall remained silent. The concept of cerebral symmetry would be displaced by mounting clinical evidence for the hemispheres being functionally different, but neither Gall nor Bichat would live to witness the advent of the concept of cerebral dominance.