Of all the special questions which have arisen about the localization of functions in the nervous system, that of the function of certain areas known as "motor centres" has been eagerly discussed. The region on both sides of the fissure of Rolando in Fig. 3 contains a number of areas which give, when stimulated with electricity, very definite and regular movements of certain muscles on the opposite side of the body. By careful exploration of these areas the principal muscular combinations--those for facial movements, neck movements, movements of the arm, trunk, legs, tail, etc.--have been very precisely ascertained. It was concluded from these facts that these areas were respectively the centres for the discharge of the nervous impulses running in each case to the muscles which were moved. The evidence recently forthcoming, however, is leading investigators to think that there is no cortical centre for the "motor" or outgoing processes properly so called, and that these Rolandic areas, although called "motor," are really centres for the incoming reports of the movements of the respective muscles after the movements take place, and also for the preservation of the memories of movement which the mind must have before a particular movement can be brought about (the mental images of movement which we called on an earlier page Kinaesthetic Equivalents). These centres being aroused in the thought of the movement desired, which is the necessary mental preparation for the movement, they in turn stimulate the real motor centres which lie below the cortex at the second level. This is in the present writer's judgment the preferable interpretation of the evidence which we now have. [Illustration: FIG. 5.--The speech zone (after Collins).]