In the last two chapters we have talked about the arrangement of the nervous system and its working as seen in simple reflex actions, and the special activities of the brain which make up the intellectual processes and the emotions. Before we can leave the subject of nervous activity, there are some special kinds of reflexes to be spoken of, and there are also some additional things to say about the working of the emotions. When we speak of special reflex actions we have in mind some of the most useful of our own reflexes. They are not different from the simple reflexes that are described in Chapter X, except that they involve a larger number of sense organs and many muscles, and are correspondingly more complicated. Furthermore, on account of this complication a special part of the nervous system is devoted to carrying them on. Back in Chapter VIII, under the heading of motion, the different types of bodily movement were listed. Chief of these was the act of locomotion; that is, the means by which we get from one place to another, an act which is, of course, of prime importance in maintaining life, since it is concerned both with the securing of food and the escaping of harm. Locomotion is performed in a number of different ways; in ourselves, walking, running, leaping, swimming, riding a bicycle are all forms of locomotion. Any of these acts, as stated in Chapter VIII, requires the accurate timing and accurate grading of the contractions of a great many different muscles. As we saw in that same chapter there are special sense organs which furnish the information upon which this accurate control of the muscles of locomotion is based. We have now to consider the part played by the nervous system in carrying it on. Whenever one starts to walk or to perform any of the other acts of locomotion, nervous disturbances will be set up in great quantity from the organs of muscle and joint sense in the parts of the body that are active, and also from the organs of equilibrium in the ear. It is necessary that the whole volume of nervous disturbance that is pouring into the central nervous system from these sources be translated into a series of streams of disturbances passing out over the motor nerves to cause the muscles to work just as they should in performing the act. All this is reflex in the strict sense. That is to say, the muscular action follows the arousing of the sense organs with no more delay than is necessary for the passage of the nervous disturbance. The work of transforming the incoming stream into a suitable outgoing stream is performed by a part of the brain about which little has been said thus far, namely the _cerebellum_. This is connected with other parts of the central nervous system in such a way that pathways from organs of equilibrium and from the organs of muscle and joint sense lead into it. From it in turn come a great many connecting nerve cells whose axons pass along the spinal cord and form