Entrance of chyle into the lacteals. The lacteals begin at a club-shaped lymphatic space lying in the center of the villus, and connected with the smaller lymphatic spaces of the adenoid tissue around it; it opens below into the submucous lymphatic plexus from which the lacteals spring.
The thoracic duct is the common trunk which receives the absorbents from both the lower limbs, from the abdominal viscera, from the walls of the abdomen, from the left side of the thorax, left lung, left side of the heart, and left upper limbs, and from the left side of the head and neck. It is from fifteen to eighteen inches long in the adult, and extends from the second lumbar vertebra to the root of the neck. At the last dorsal vertebra there is usually a dilation of the duct, of variable size, which is called the receptaculum chyli, and is the common place of junction of the lymphatics of the lower limbs and the trunks of the lacteal vessels. There are two sets of absorbent vessels—the lacteals, which convey the chyle from the alimentary canal to the thoracic duct; and the lymphatics, which take up the lymph from all the other parts of the body and return it into the venous system. There is a right lymphatic duct, about a quarter to a half inch in length, which receives the lymph from the absorbents of the right upper limb, the right side of the head and neck, the right side of the chest, the right lung and the right half of the heart, and the upper surface of the liver. The thoracic duct terminates on the outer side of the internal jugular vein, in the angle formed by the union of that vein with the subclavian, and the subclavian empties itself in the superior vena cava.
Lymphatics and lacteals are furnished with valves serving the same office as those of the veins, and for the most part constructed after the same fashion.
Lymph and chyle, unlike the blood, pass only in one direction, namely, from the fine branches to the trunk and so to the large veins, on entering which they are mingled with the stream of blood and form part of its constituents.
In some part of their course all lymphatic vessels pass through certain bodies called lymphatic glands.
Analysis of lymph and chyle:
| Lymph. | Lymph from Thoracic Duct. | Chyle from the Lacteals. | ||||
| Water, | 937 | .32 | 939 | .70 | 902 | .37 |
| Fibrine, | 0 | .595 | 10 | .60 | 3 | .70 |
| Albumen, | 42 | .775 | 38 | .83 | 35 | .16 |
| Fat, | 6 | .51 | a little | 36 | .01 | |
| Extractive Matter, | 5 | .05 | ||||
| Salts, | 7 | .75 | 10 | .87 | 22 | .76 |
| 1000. | 1000. | 1000. | ||||
Chyle having reached the lymphatic channels, its onward progress is determined by a variety of circumstances. Putting aside the pumping action of the villi, the same events which cause the movement of the lymph generally, also further the flow of the chyle, and these are briefly as follows:
1. The wide-spread presence of valves in the lymphatic vessels causes every pressure exercised on the tissues in which they lie, to assist in the propulsion forward of the lymph.