In the two or three following years the rest of the lymphatic system was discovered by Rudbeck in Sweden, by Bartholin in Den mark, and by Jolyfl'e in this country ; nor was it long before the function of absorption was ascribed to it by Glisson, in 1654, and by Hoffmann. Since this period, we have been in debted for various details of the arrangement of this system of vessels in man and other Main malia, in Birds, in Reptiles, and Fishes, to numerous investigators, Nuck, Ruysch, Albi nos, Steckel, Hunter, Monro, Howson, Cruick shank, Scemmerring, Mascagni ; and in the pre sent day to Fohmann, Laud), Lippi, Rossi, Panizza, and other continental anatomists.
The lymphatic vessels in the human subject are exceedingly delicate and transparent tubes, numerous but small, existing in most if not in every part of the organism, crowded with valves, and terminating, after passing through the glandular bodies, in two princi pal trunks, through which the contents of the whole system are emptied into the circulating venous blood at two corresponding points not far distant from the heart, viz. at or close to the angles of union between the subclavian and internal jugular veins. The two trunks of the lymphatic system are by no means symme trical. That which enters the veins ou the left side measures as much as sixteen or eighteen inches in length in the adult human subject. It commences in the abdominal cavity by a slightly marked dilatation, the receptaculum chyli, into which the chyl iferous vessels pour their contents; it then passes through the thorax to reach its termination in the neck. This trunk is usually termed the thoracic duct ; it may be said to receive the lymph of three-fourths of the body, together with the whole of the chyle. The right lymphatic trunk is about two lines in diameter, very short, corresponding in situa tion and length to the last half-inch of the left trunk ; consequently it will only be found at the root of the neck, close to the point of its termination. This trunk receives the remaining fourth of the lymph, viz. that collected from the right upper fourth of the body. Professor Lippi published a work on the lymphatic system in the year 1825, in which he described in the human subject many terminations of the lymphatics in other parts of the venous sys tem, especially in the vena cava inferior, the vena portn, and the principal branches by which these vessels are formed, but subsequent observers have not corroborated his views. The vessels which Professor Lippi saw joining other large venous trunks were evidently the returning veins of the conglobate glands, into which the injection received by the lymphatics had passed during its transit through the glands : —a fact of extreme interest, and to which we must recur in speaking of the structure of the glands, but which has been observed by every anatomist who has had much practical experi ence in injecting the lymphatic system. Lippi
would have been perfectly correct, how ever, had he confined his statement to what takes place in Birds, Reptiles, and Fishes.
The lymphatic vessels resemble the veins in possessing valves, and in conveying their contents from branch to trunk ; moreover their internal tunics are continuous where the one set of vessels joins the other. In their mode of distribution also throughout the body the analogy between the two systems is consi derable. Eustachius,when he first saw the prin cipal trunk of the lymphatics, from its being filled with chyle, at once described it under the name of the vena alba thoracis, and many have considered the lymphatic vessels as an appendage to the venous system, rendering it more perfect. Although we are warranted in saying that the lymphatic vessels convey their contents from branch to trunk, by which is generally understood from smaller and more numerous to larger and less numerous vessels, as is the case with the veins; yet is there- an other principle apparently of an opposite kind observed in their distribution, by which the in fluence of capillary attraction is engaged in the important service of moving onward their con tents, at the same time that these are ex posed to a larger surface of the containing vessels, from which in all probability they derive some essential modification. This admirable and simple provision is especially evident in the lower extremities, where the greatest resis tance from gravity is to be overcome. A vessel on the instep, for instance, of half a line in diameter, instead of emptying itself into a larger one as it proceeds upwards, bifurcates into vessels of equal diameter with itself; each of these again will in a similar manner sub divide, until at length by a series of dicho tomous divisions, although some reunions may take place, this single vessel has multiplied itself by the time it reaches the inguinal region into as many as fifteen or more branches, each of the same diameter or nearly so as the ori ginal branch on the instep. Indeed, through out the lymphatic system, we scarcely find a branch of more than an inch in length whow diameter is not within the range requisite for the production of capillary attraction. The thoracic duct itself, which is two or three lines in diameter, may be said to form an exception, hut the onward progress of its contents is specially provided for by its juxtaposition to the aorta, from which circumstance it is sub jected during life to an alternating pressure of considerable force, and fully competent in a vessel provided with valves to ensure the ad vance of its contents.