389. The LYMPHATIC VESSELS, in structure, resemble the lacteals. They exist in great numbers in the skin and mucous membranes, particularly those of the lungs. Though no lymphatics have been traced to the brain, it is presumed that they exist there, as this part of the body is not exempt from the composition and decomposition, which are perpetual in the body. These vessels are extremely minute at their origin, so that in many parts of the system they cannot be detected without the aid of a microscope. -=-=-=-=-=-=-=-=-=-=-=-= 387. Define absorption. 388-391. _Give the anatomy of the lymphatic vessels._ 388. What are those vessels called that act exclusively for the growth and renovation of the body? Those whose office is to remove the atoms already deposited? What other vessels perform the office of absorption? Give observation. 389. Describe the lymphatics. -=-=-=-=-=-=-=-=-=-=-=-= [Illustration: Fig. 82. A single lymphatic vessel, much magnified.] [Illustration: Fig. 83. The valves of a lymphatic trunk.] [Illustration: Fig. 84. 1, A lymphatic gland with several vessels passing through it.] 390. The lymphatic vessels, like the veins, diminish in number as they increase in size, while pursuing their course toward the large veins near the heart, into which they pour their contents. The walls of these vessels have two coats of which the external one is cellular, and is capable of considerable distention. The internal coat is folded so as to form valves, like those in the veins. Their walls are so thin, that these folds give them the appearance of being knotted. -=-=-=-=-=-=-=-=-=-=-=-= What is represented by fig. 82? By fig. 83? By fig. 84? 390. In what respect do these vessels resemble the veins of the system? Give the structure of their coats. -=-=-=-=-=-=-=-=-=-=-=-= 391. At certain points, the lymphatic vessels pass through distinct, soft bodies, peculiar to themselves, which are called _lymphatic glands_, which are to these vessels what the mesenteric glands are to the lacteals. The lymphatic glands vary in form and in size. They are extremely vascular, and appear to consist of a collection of minute vessels. These glands are found in different parts of the body, but are most numerous in the groins, axilla, or arm-pits, neck, and cavities of the chest and abdomen. _Observation._ From exposure to cold, these glands are frequently enlarged and inflamed. They are known under the name of "kernels." They are often diseased, particularly in scrofula, or "king's evil." PHYSIOLOGY OF THE LYMPHATIC VESSELS.