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Show Tbs Termination (f HM Lactmls rmd Lympbmit's. Tbe Tgrmz'nalitw oft/w Laclcals and Lympbrztics. The thoracic duct in the human subject may be sixteen, eighteen, or twenty inches in length. The second trunk of the absorbents, or that which terminates in the jugular and subclavian of the right side, is fre- quently not more than a quarter of an inch in length; it lies upon the superior surface of the right subclavian, and terminates in the angle between it and the jugular of the same side; its diameter is not inferior to that of the thoracic duct, at the same place, on the opposite side. \Vhy the lym- every titnc the right auricle contracted, more resistance would have been made to the entrance of the absorbed fluids into the veins, as there is not 96 97 phatics and lacteals terminate first in glands, l have perhaps explained. \Vhy they terminate, after this, in two large trunks is very evident : in the first place, the larger the trunks are, the stronger are the muscular fibres; in the second place, the greater is the bulk of the fluids: in consequence of both these circumstances, the more certainly will the absorbed fluids overcome the resistance made to their entrance into the subclavian veins by the blood. \Vhy they terminate at last in the jugular and subclavian veins is also very evident; for in the veins, the motion of the blood is slower, and the resistance, of course, less than it would have been in the arteries. Why they terminate in the angles between the jugulars and sub- clavians, is also evident; for the resistance of the blood to any fluid enter- ing the veins must be less, as that blood comes nearer the heart. Why they enter at the angle is also evident; because the columns of blood in thejugulars opposing those of the subclavians with nearly equal force, the venous blood at this place must flow in the diagonal between the beginnings of these two veins, and the absorbed fluids, of course, in the same direction as the current of blood in this place. The reason of the thoracic duct forming a curve, and descending to its termination, would seem to be. to give its fluids the advantage of their gravity, by which they may more only always more or less retardation of the blood‘s motion in the cava superior, every time the right auricle contracts, but there is even retrograde motion, which is greater in proportion as the blood is nearer the auricle. Thus the thoracic duct, and the second trunk of the lymphatics, are both inserted with the greatest possible advantages. This last argument, as well as that adduced for the termination of the lymphatics in the angle between the jugulars and subclavians, are those employed by Dr. Fordyce, The reason also why the thoraCic duct is inserted into the left subclavian, in preference to the right, seems to be not merely that the former is nearer the duct, but because the fluid coming from the left subclavian is not in so direct a line with the eava superior as that front the right subclavian is; the retrograde motion in the blood, on the contraction of the auricle, will, of course, affect it less. That part of the left subclavian, lying under the sternum, slopes gradually towards its insertion into the cava superior; and the absorbed fluids, both in the erect and horizontal position of the body, from this circumstance, descend, assisted by their own gravity, into the heart. Morgagni employs a similar argument for the termination of the thoracic duct as now described, and against the propriety of any other ter- mination, viz. If the lymphatic vessels had been inserted into the cava inferior, they would have increased the quantity of fluids in that vessel mounting upwards against their own gravity. This argument, he says, was first suggested to him, from Cowper's reasoning on the propriety of nature's forming the vena azygos; which, he says, was in order to diminish the quantity of blood, which otherwise must have mounted upwards in the easily overcome the resistance made to their entrance by the venous blood; cava. but they would lose more force from altering their direction, than they would gain by this addition from their gravity. The absorbed fluids are not discharged into any other veins; and the reason of this is also evi- primo cognita est, non parum fateor placuisse, sive quod revera habeat Cur dent; for, from their greater accumulation in the thoracic duct, their mo- ramum superioris iullthrc."--Hallcr not only supports the propriety of the mentum is increased, and they are enabled more readily to overcome the terminations as we have described them, but he combats the doctrine of resistance from the venous blood. those anatomists who maintained other insertions of lymphatics into red The reason also why they do not termi- nate nearer the heart, or in the cava superior, is also evident; for then, every Morgagni‘s words are, " Quam quidem sententiam cum mihi ea placere dcbeat, sive quod similes ob cattsas ipse olim conjecissem thoraci- cum quoque ductum, non in proximam venam cavam inferiorem, sed in veins. Professor Mckel, in particular, warmly contends for such termina- O iiUHS : |