Their use is the same as in the veins, viz. to permit the ascent of the fluid, and to prevent its return; but they do not always fully do this. Injection often without difficulty overcomes some of them. In dropsies, in which the absorbents are full, if we raise the skin, we easily distinguish these vessels by their transparency; but soon, notwithstanding their valves, they become empty, and then cease to be visible. Different anatomists have forced air, and even other fluids, into a great number of the lymphatics, by means of the thoracic duct, and consequently in an opposite direction to their valves. All these phenomena do not suppose in these vessels, as in their common duct, varieties in the structure of the valves, in their width, &c. but only different degrees of dilatation and contraction, degrees that are, as I have said, independent of structure. In dilatation, the valves close the caliber less than in contraction. The valves of the absorbents have the same form and the same arrangement as those of the veins; they partake, by their constant exemption from ossification, of the general character of the membrane from which they arise, and which, by folding, forms them. ARTICLE SECOND. LYMPHATIC GLANDS. I. _Situation, Size, Forms, &c._ These glands are scattered in the different parts in greater or less number. In the superior and inferior extremities, we find but a small number, except at the upper parts, the axilla and the groin. In the ham and at the elbow there are some, and there are engravings of them at the instep. But upon the arm, the leg, the thigh, the fore-arm, &c. they are not found. It is about the articulations that all are met with; in this respect, we can say, that they are constantly increasing from the inferior to the superior, no doubt because in ascending the number of absorbents is continually increasing. Not numerous on the cranium, they are only on the exterior of this cavity, no one has ever, I believe, been found within it; which proves, perhaps, that it is not the tenuity of the absorbents that conceals them from us there, but that it is because they are of a peculiar nature and different from that of the others. The face contains many of these glands, especially along the stenonian duct, upon the buccinator, &c. As to the trunk, if we take the vertebral column for a term of comparison, we shall see that there are but very few lymphatic glands, hardly any at its posterior part, and that they are very numerous anteriorly. On the neck, the jugulars are accompanied by a great series of these glands. In the thorax, the posterior mediastinum contains many of them. In the abdomen, they are abundant along the vertebral column, behind the mesentery.