LYMPHATIC AND LACTEAL SYSTEM. 



207 



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 portoe, 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 whose 

 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, 

 but the onward progress of its contents is 

 specially provided for by its juxta-position 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. 



The principal lymphatics in any part of the 

 body may be said, taken collectively, to equal 

 the capacity of the arteries or veins of the same 

 part ; thus, in the inguinal region the sum of 

 the diameters of the lymphatic vessels may 

 equal the diameter of the main channel by 

 which the venous blood is returned from the 

 lower extremity ; but by this simple subdivision 

 of the outlet for the lymph into numerous 

 branches, that almost universal, and, in its 

 effects, wonderful power, by which the nutrient 

 fluid throughout the vegetable creation is car- 

 ried from the lowest fibril of the root to the 

 highest living point in vegetable existence, is 

 made available in the progression of the lymph in 

 animals towards the centres of the system. This 

 disposition of the lymphatic vessels throughout 

 their course necessitates a greater uniformity in 

 point of size, than we find to hold good with 

 the artery or vein, and indeed constitutes their 

 chief peculiarity in distribution when com- 

 pared with the other divisions of the vascular 

 system. The arborescent appearance, except 

 on the surface of the liver and spleen, is 

 scarcely to be met with in the lymphatics ; they 

 almost always form a net-work of vessels, the 

 meshes of which vary both in form and size 

 in the different organs and in different parts 

 of the body ; as a general rule, when the 

 vessels have a short course to run, the spaces 

 they enclose are small and more nearly equi- 

 lateral ; but when the contrary is the case, as 

 occurs in the extremities, the meshes are very 

 large and much elongated, so that the vessels 

 run nearly parallel with each other, and the 

 net-work arrangement is scarcely perceptible; 

 there is, however, still less appearance of arbor - 

 escence. 



In this respect the lymphatics may be said 

 to resemble more the capillary bloodvessels, 

 which in the web of the frog's foot, or in the 

 vesicular lungs of the salamander, toad, or frog, 

 are so plainly seen to form a net-work of nearly 

 equal-sized vessels, and, indeed, to cease to be 

 capillaries when they become arborescent. 



Another peculiarity in the disposition of the 

 lymphatic vessels occurs at their approach to a 

 conglobate gland, through which their contents 

 are to be conveyed. The vessels leading to a 

 gland which are termed the vasa inferentia or 

 afferentia of the gland, vary in number, being 

 seldom less than two, and rarely amounting to 



