Observe that nature is not confined to any methodical order, in distributing these systems in the different apparatus; that she has no regard to the great differences that she has established between the functions. Each can at the same time belong to the apparatus of functions that have no analogy. Thus the fibro-cartilaginous, which is found especially in the organs of locomotion, and consequently in animal life, enters also by the trachea into the respiratory apparatus; thus the mucous system, everywhere destined to the organs of internal life, belongs also to the external life in the conjunctiva, in the nasal fossæ, &c. to generation in the vesiculæ seminales, in the prostate, &c.; thus the glandular system pours by turns fluids upon the organs of the two lives as upon those of generation; thus the serous surfaces are spread upon parts whose functions have no resemblance upon the brain and the stomach, for example, upon the articular cartilages and the lungs, &c. Let us consider then the simple systems abstractedly, if I may so say; let us describe them in an insulated manner as materials distinct from each other, though united two by two, three by three, four by four, &c. to form the partial edifices of our apparatus, edifices from which results the general edifice of our organs. Each of these apparatus is destined to exercise a determinate function, and ought consequently to be classed as functions; it is in this manner also that we shall distribute them in the Descriptive Anatomy. But the simple systems, not tending to a common object, except as they are united in the apparatus, we cannot, when considering them separately, confine them to any classification borrowed from their destination. OSSEOUS SYSTEM. This system, remarkable among all the others by the hardness and resistance that characterize it, has from this double attribute a fitness to serve as a common base for all, upon which they rest, and around which they are suspended and fixed. The whole of the pieces that form it, are connected together for this use, by means of flexible and resisting bands, which with these pieces make a whole that is called a skeleton. The osseous whole, placed in the midst of many organs that it sustains, everywhere continuous in its different parts, has not however, like the primitive systems, continuity of peculiar life from one of its extremities to the other. The bands which connect these different pieces, very different from them in their nature and their properties, produce in them an insulation of vitality, which the different parts of the above systems do not exhibit, because in their continuity their nature is everywhere the same. ARTICLE FIRST. _Of the Forms of the Osseous System._