The muscular fibre is red, soft, of an uniform size in the great and small muscles, sometimes disposed in very evident fasciculi and separated from each other by remarkable grooves, as in the gluteus maximus, the deltoid, &c. sometimes more equally in juxta-position, as in most of the broad muscles, always united to many others of the same nature like it, easily by this union distinguished by the naked eye, but eluding microscopic researches when we wish to examine it in a separate manner, so great is its tenuity. Notwithstanding this extreme tenuity, an infinite number of researches have been made during the last age, to determine with precision the size of this fibre. On this point may be read the result of the labours of Leuwenhoek, Muysk, &c. I shall not give here this result, because science can draw nothing from it, and because we cannot rely upon its accuracy; of what importance moreover is the precise size of the muscular fibre? its knowledge would add nothing to our physiological views upon the motion of the muscles. Every muscular fibre runs its course without bifurcating or dividing in any manner, though many have thought otherwise; it is found only in juxta-position to those which are near it, and not intermixed, as often happens in the fibrous system; an arrangement that was rendered necessary by the insulated motions it performs; for the general contraction of a muscle is the union of many partial contractions, wholly distinct and independent of each other. The length of the fleshy fibres varies very much. If we examine in general the mass which they form by their union, we observe that this mass has sometimes much greater extent than the tendinous portion of the muscle, as the biceps, the coraco-brachialis, the rectus internus femoris, &c.; that sometimes its length is much less as in the small plantar and palmar muscles, &c.; and that sometimes it is about equal, as in the external radial, &c. If from the examination of the fleshy mass, we pass to that of the separate fibres that compose it, we see that the length of the first is rarely the same as that of the second. There are hardly any but the sartorius and some analogous muscles, whose fibres run the whole extent of the fleshy, mass; in almost all the others, they are found obliquely arranged between two aponeuroses, or between a tendon and an aponeurosis; so that though each of them may be very short, as a whole they are very long, as we observe in the anterior rectus of the thigh, the semi-membranosus, &c. This arrangement may also arise from various tendinous intersections, which cut at different distances the length of the fibres. In general, the muscles which owe their length to long fibres, have great extent and very little power of motion; whilst those with short fibres, but multiplied so as to give great length as a whole, are remarkable for an opposite character. And this is the reason: all the fibres being