CHAPTER XII. 



VASCULAR SYSTEM CONCLUDED: LYMPHATIC VESSELS AND 

 LYMPH. LYMPHATIC GLANDS AND BODIES OF ALLIED 

 STRUCTURE. 



The lymphatics. — In addition to the blood-vessels, which form 

 a continuous series of tubes for the passage of the blood, there 

 is another system of vessels in the body, which arise in the 

 different tissues, and pour their contents into the great veins 

 near the heart. The fluid which these vessels contain is ab- 

 sorbed from the tissues, and is called, from its transparent 

 watery appearance, " lymph " (lympha^ water), while the ves- 

 sels themselves are known as lymphatics. 



The lymphatics may be divided into two sets : the lacteals, 

 which take up the milk-like fluid, called chyle, from the intes- 

 tines and carry it to the thoracic duct ; and the lymphatics 

 proper, which drain off the lymph from all parts of the body 

 and return it to the blood through the thoracic and right lym- 

 phatic ducts. These two sets of vessels, however, are alike in 

 structure, and will be considered together under the general 

 name of lymphatics. 



The lymphatics are found in nearly all the tissues that are 

 supplied with blood. The larger trunks usually accompany the 

 deep-seated blood-vessels, and the smaller vessels form networks 

 in all parts of the body where the extensively distributed and 

 penetrative connective tissue is found. 



The lymphatics have their origin in the connective tissue. 

 They may be said to begin as irregularly shaped or tubular 

 spaces in the areolae, and are distinguished from the lymph 

 spaces in the tissue outside by being lined with a single layer 

 of flat, transparent endotheloid cells having a peculiar den- 

 tated outline, by means of which they are readily recognized. 



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