An attempt has been made to put the question in a more precise and limited form by studying the brains of men distinguished in different lines. But this method, in avoiding the difficulty, answers our question indirectly only. Most often great inventors possess qualities besides imagination indispensable for success (Napoleon, James Watt, etc.). How draw a dividing line so as to assign to the imagination only its rightful share? In addition, the anatomical determination is beset with difficulties.
A method flourishing very greatly about the middle of the nineteenth century consisted of weighing carefully a large number of brains and drawing various conclusions as to intellectual superiority or inferiority from a comparison of the weights. We find on this point numerous documents in the special works published during the period mentioned. But this method of weights has given rise to so many surprises and difficulties in the way of explanation that it has been quite necessary to give it up, since we see in it only another element of the problem.
Nowadays we attribute the greatest importance to the morphology of the brain, to its histological structure, the marked development of certain regions, the determination not only of centers but of connections and associations between centers. On this last point contemporary anatomists have given themselves up to eager researches, and, although the cerebral architecture is not conceived by all in the same way, it is proper for psychology to note that all with their "centers" or "associational system" try to translate into their own language the complex conditions of mental life. Since we must choose from among these various anatomical views let us accept that of Flechsig, one of the most renowned and one having also the advantage of putting directly the problem of the organic conditions of the imagination.
We know that Flechsig relies on the embryological method--that is, on the development--in the order of time, of nerves and centers. For him there exist on the one hand sensitive regions (sensory-motor), occupying about a third of the cortical surface; on the other hand, association-centers, occupying the remaining part.
So far as the sensory centers are concerned, development occurs in the following order: Organic sensations (middle of cerebral cortex), smell (base of the brain and part of the frontal lobes), sight (occipital lobe), hearing (first temporal). Whence it results that in a definite part of the brain the body comes to proper consciousness of its impulses, wants, appetites, pains, movements, etc., and that this part develops first--"knowledge of the body precedes that of the outside world."