This relation of the trunks and the branches has been exaggerated however by mathematical physiologists, who attributed to the last over the first a predominance much greater than really existed. A cause of error upon this point may arise from measuring the arteries at their exterior after having injected them; in fact, the caliber of the trunks is greater, in proportion to their parietes, than that of the branches separately examined; that is to say, other things being equal, the aorta has parietes thinner in proportion to its cavity, than the cubital artery; hence, without doubt, why aneurisms are rare in the branches, and frequent in the trunks, especially when the diseases arise from a local cause; for if they are the effect of a general disease, oftentimes the little arteries, the radial particularly, are also affected; I have already seen two examples of it. This observation upon the proportions of the arterial parietes proves the impossibility of judging of the relations of diameter between the two, at least by examining them in the interior. Besides, these relations are necessarily very variable, according as the vital forces which vary themselves so much, increase or contract the caliber of the small arteries; and in this point of view, this examination cannot have the importance that was attached to it by the ancients, whose works are filled with calculations upon this point. III. _Termination of the Arteries._ After being divided, subdivided, and having the peculiarities we have just examined, the arteries terminate in the general capillary system. To point out where this system begins, and where the arteries end, would be very difficult. We can prove that there the blood ceases to be entirely under the influence of the heart, and circulates by the influence of the insensible organic contractility of the vascular parietes; but how can this line of demarcation be rendered evident to the eye?