equally large, whatever may be their length, have the same degree of force; it is evident then that this force considered in a muscle as a whole, is measured by the number of its fibres. On the other hand, the longer a fibre is, the more it shortens in its contraction; then by contracting, a muscle brings its attachments so much the nearer in proportion as its fibres are longer. All the fibres of the voluntary muscles are straight, those of the sphincters excepted. They are either parallel as in the rhomboids, or obliquely situated in relation to each other, as in the great pectoral. Sometimes in the same muscle many sets cross each other in different directions, as we see in the masseter; but this crossing is wholly different from that of the involuntary muscles in which there is more crossing of fibres, whilst here we see only fasciculi in different directions, in juxta-position to each other. I shall not speak here of the cylindrical form according to some, and the globular one according to others, of the fleshy fibre; inspection teaches us nothing upon this point; how then can we make that an object of research and give an opinion upon it, which has no real foundation? Let us say thus much of the intimate nature of this fibre, upon which so much has been written. It is unknown to us, and all that has been said upon its continuity with the vascular and nervous extremities, upon its pretended cavity, upon the marrow, which according to some filled it, &c. is only a collection of vague ideas, which nothing positive confirms, and to which a methodical mind would not attend. Let us begin to study nature where she begins to come under our senses. I would compare the anatomical researches upon the intimate structure of the organs, to the physiological researches upon the first causes of the functions. In both we are without guides, without precise and accurate data; why then give ourselves up to them? All that we can know upon the nature of the muscular fibre, is that it is peculiar, that it is not the same as that of the nerves, nor as that of the vessels, nor as that of the tendons or the cellular texture; for where there is identity of nature, there ought to be identity of vital properties and of texture. Now we shall see that all these systems differ essentially from each other in this point of view; there can be between them no analogy in relation to their nature, whence the properties are always derived.