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Show TIM Valves (y‘ the Lactealr and Ly/nplmticr. Tbe Valves If tbe Laclmlx (111d Lynzp/mtics. ding phatic vessel by its circular edge, having its straight edge, correspon this of ce consequen in cavity: the in floating or loose, to the diameter, to the lymphatic vessel. The same valves are to be observed when a lymphatic vesscljoins the thoracic duct, to prevent the contents of the thoracic duct from passing retrograde into the branches. It is from this cir- cumstance that the thoracic duct, injected with wax, appears as a trunk 66 lie close to the contrivance, iluids passing in one direction, make the valve in the side of the vessel, and leave the passage free ; but attempting to pass its push and vessel, the of side the from valve the raise direction, opposite loose edge toward the centre ofthe cavity: but, as this would shut up little more than one half of the cavity, the valves are disposed in pairs, exactly opposite to each other, by which means the whole cavity is accurately closed. Their loose edges are constantly turned towards the thoracic duct, or trunk of the system, so that fluids may pass towards it, but cannot escape from it into the branches. It is principally by means of these valves that we so readily distinguish lymphatic vessels from arteries and veins, or any other vessel. The arteries have none, except at their beginnings; the veins have none, or next to none, in the brain, viscera of the thorax, and viscera of the abdomen. Even on the extremities, where the veins have valves, they are never so eroudcd as in the lymphatics. No other vessels in the body have valves. 1 have said that the valves are placed in pairs; they are also frequently found intersecting the vessels, at equal distances, about the eighth or sixteenth part of an inch apart. There is great variety, how- ever, in their distribution, in different bodies: the thoracic duct, for example, in some bodies, has perhaps only three or four pair of valves; in others,I have seen it crowded with valves throughits whole length. I have seen a lymphatic vessel run six inches, without a single valve appearing in Sometimes the trunks are more crowded with valves than the its cavity. branches, and sometimes I have seen the reverse of this. It is not neces- sary to open the vessels, in order to discover the valves; they are suffi- ciently marked on the outside, and give the vessels the appearance of being notched or jointed in different places. The lacteals are generally strongly marked in this way, which makes them at times resemble a string of beads. 67 without any branches; and that, when injected with quicksilver, and viewed with a magnifying glass, it appears externally rough and tuberculated: the tubercules are the projections made by the valves, at the beginnings of the branches. In the red veins we sometimes meet with three or four valves, in- stead oftwo, in one place. In the lymphatics I never saw more than two; and frequently, where a lymphatic enters a red vein, there is but one valve.- The thoracic duct itself was thus described by its discoverer Eustachius, as we have seen :-" Ostiolum semicirculare in ejus origine, is the expres- sion he employs. This I have seen in quadrupeds, but never in the human subject, where there are constantly a pair of valves. however, has confused other anatomists. This description, Haller, in particular, seems in- determined in a matter of the greatest simplicity. In his description of these valves, he says, " Ipsa autem valvula membranas habet a ductu chy- lifcro undique in vcnam procurrentes ad circularis hymenis speciem, quem pro (lual)us valvulis potius quam pro una semilunari habeas." The vast number ofvalves notonly distinguish and characterise the absorbent vessels from all others in the human body, but also in quadrupcds, birds, amphia biotis animals, fish of warm blood, as they are stiled, and even in fish of cold blood. Mr. I-Icwson says nothing of the valves in the lymphatics of birds, in that part of his book where he particularly describes the sys- tem; but in another part of the same book, speaking of injecting the villi of the intestines in birds, he says, " the experiment is more difficult, because their lacteals are full of valves, and their villi are small, compared to those of the turbot: nevertheless, I have succeeded, in getting the valves to give markable: nor is there the least reason for eensuring Ruyscli and Nuck on way, so as to fill a few of the lacteals distinctly enough to be seen to divide into branches upon the villi."--ln the turtle they are very evident in the lactcals on the mescntery, and with some difficulty forced, by pressing the this subject, as having, in their engravings, very much exaggerated it. quicksilver injected from the trunk, pretty firmly, with the finger close to Wherever a lymphatic vessel enters a vein, there is always a valve, and most commonly a pair, to prevent the blood from passing from the vein in~ the valves, and in the direction of the intestines. In this way I have often ruptured the valves, without rupturing the vessels, and made the injection In the lymphatic vessels of quadrupeds, this appearance is also very re- K 2 t0 pass |