When a branch arises from a trunk, the circular fibres of the last separate and form on each side a half ring, whence arises a complete one, which embraces the small rings formed by the circular fibres of the arising branch. These circular fibres go even to the eminence of the common membrane, which is seen within the arterial cavity and of which I have spoken; so that the whole thickness of the peculiar membrane serves as a support to their origin. But there is but little continuity between the two kinds of fibres. Those of the branch do not arise from those of the trunk; it is the internal membrane that serves to fix them together, as fibres of communication. Dissection shows easily these branches set at their origin in the ring which arises from the separation of the circular fibres. We remark this at the origin of the intercostals and lumbars upon the aorta, &c. When two trunks of an equal size go off, as the iliacs, the last circular fibres of the primitive trunk which they formed, interlace intimately with the origin of each of the two circular layers, that arise at the fork that separates this origin. Thus the last rings of the aorta cannot be separated from the first of each iliac. There are no longitudinal fibres in the arteries. What is the nature of the arterial fibre? Almost all anatomists have considered it the same with the muscular. But if we examine them attentively, it is easy to be convinced of their differences. The want of red colour does not establish these differences, since in man even, some parts really muscular, as the intestines, want this colour. But the muscular texture is soft, loose and very extensible; the arterial texture on the contrary is firm and solid, breaks before it yields. We can observe this, by tying an artery tight. The two internal coats are cut; the cellular alone is not, though the ligature is immediately applied to it; we observe, by opening the artery, a section corresponding with the thread, exactly similar to what a cutting instrument would have made. I have often repeated this experiment, pointed out by Desault, upon the dead body, and upon living animals; the result which is very uniform, explains the frequency of hemorrhages after the operation for aneurism. There is undoubtedly no texture so brittle, if I may use the word, as the arterial, none consequently less proper to be embraced by ligatures. Why is it that this should be the only one in which it is necessary to apply them? This phenomenon alone would distinguish the arterial texture from the muscular. In fact, the preceding experiment, made upon a portion of intestine in which the fibres are arranged like the arterial, would produce a flattening, an approximation of these fibres, but would not cut them.