CHAPTER XII. STRUCTURE OF THE BODY. Some study of the structure and activities of the body-which is an A knowledge of the body necessary to a full knowledge of the mind— Its structure to be studied before its functions-Systems, organs, tissues, and cells-Organs of sense-The nervous axis-Rudimentary structures-Symmetrical relations and homologies. HAVING, in the last section, justified our natural confidence. in the testimony of the senses and understanding about the external world, we may now securely proceed to the investigation of our own nature and the world about us, commencing with the former. ledge of necessary The object of this work being an inquiry after truth, it A knowmust, of course, always be more or less directly concerned the body with human thought, since "truth" consists in an accurate to a full correspondence between thought and things external.* knowledge the present section it is proposed to apply ourselves. In of the mind. especially and directly to the examination of thought and of all human mental activity. But "thought," as we know it, is only carried on by the help of a living body and depends for its continuance on that body's life, and therefore on the due performance of those bodily activities without * See below, chap. xvii., "Objectivity of Truth." L Its structure to be studied before its functions. which life cannot be maintained. To have anything like a full comprehension of our powers of thinking, then, we should be acquainted not only with the inferior forms of our mental activity, but also with those bodily activities which are thus indispensable for their performance. But it is impossible to understand how any structure or mcchanism acts, unless we also know something of the order and arrangement of its parts. Therefore, we cannot adequately understand the human mind, unless we are somewhat acquainted with the structure of the human body, and with the different kinds of activity it displays. The human body is obviously a complex structure, consisting of different parts, which act in different ways and reciprocally minister to one another. Thus, for example, the actions of the organs of sense, and of the limbs, serve to convey food into the interior of the body, where it is converted by the digestive organs into nutriment, which is distributed throughout our frame by an elaborate system of canals, or "vessels," and by this means those vessels themselves, as well as the digestive organs, limbs, and organs of sense, are all nourished and maintained in due working order. Thus the body is a complex whole, whereof the various parts are reciprocally ends and means, and such a body is called an “organism.” Accordingly, our body requires to be considered, for our present purpose, from two points of view, and its study needs to be followed up along two different lines of inquiry. One of these refers to its structure, and the other to the actions which it performs—that is, its "functions." As before said, a knowledge of structures must precede a knowledge of functions; and, accordingly, this chapter will be devoted to a brief statement of those main facts respecting man's bodily organization which seem needful for the comprehension of such of its functions as we are concerned with. Nothing is, of course, more familiar to us than the general external form of the human body. The leading facts as to its internal structure are also matters of common knowledge. Thus it is almost superfluous to say that beneath the skin lies the "flesh" of the body, which |