THE LYMPHATIC SYSTEM. 



fTlHE Lymphatic System includes not only the lymphatic vessels and the glands 

 J_ through which they pass, but also the lacteal or chyliferous vessels. The 

 lacteals are the lymphatic vessels of the small intestine, and differ in no respect 

 from the lymphatics generally, excepting that they contain a milk-white fluid, the 

 chyle, during the process of digestion, and convey it into the blood through the 

 thoracic duct. 



The lymphatics have derived their name from the appearance of the fluid con- 

 tained in their interior (lymplia, water). They are also called absorbents, from the 

 property they possess of absorbing certain materials from the tissues and conveying 

 them into the circulation. 



The lymphatics are exceedingly delicate vessels, the coats of which are so 

 transparent that the fluid they contain is readily seen through them. They retain 

 a nearly uniform size, being interrupted at intervals by constrictions, which give 

 them a knotted or beaded appearance. These constrictions are due to the pres- 

 ence of valves in their interior. Lymphatics have been found in nearly every 

 texture and organ of the body which contain blood-vessels. Such non-vascular 

 structures as cartilage, the nails, cuticle, and hair have none, but with these 

 exceptions it is probable that eventually all parts will be found to be permeated 

 by these vessels. 



The lymphatics are arranged into a superficial and deep set. The superficial 

 lymphatics, on the surface of the body, are placed immediately beneath the integ- 

 ument, accompanying the superficial veins ; they join the deep lymphatics in cer- 

 tain situations by perforating the deep fascia. In the interior of the body they 

 lie in the submucous areolar tissue throughout the whole length of the gastro- 

 pulmonary and geni to-urinary tracts, and in the subserous tissue in the cranial, 

 thoracic, and abdominal cavities. The method of their origin will be described 

 later, along with the other details of their minute anatomy. Here it will be 

 sufficient to say that a plexiform network of minute lymphatics may be found 

 interspersed among the proper elements and blood-vessels of the several tissues, 

 the vessels composing which, as well as the meshes between them, are much larger 

 than those of the capillary plexus. From these networks small vessels emerge, 

 which pass either to a neighboring gland or to join some larger lymphatic trunk. 

 The deep lymphatics, fewer in number and larger than the superficial, accompany 

 the dee]) blood-vessels. Their mode of origin is probably similar to that of the 

 superficial vessels. The lymphatics of any part or organ exceed the veins in 

 number, but in size they are much smaller. Their anastomoses also, especially 

 those of the large trunks, are more frequent, and are effected by vessels equal in 

 diameter to those which they connect, the continuous trunks retaining the same 

 diameter. 



The lymphatic or absorbent glands, named also conglobate glands, are small, 

 solid, glandular bodies situated in the course of the lymphatic and lacteal ves- 

 sels. In size they vary from a hemp-seed to an almond, and their color, on sec- 

 tion, is of a pinkish-gray tint, excepting the bronchial glands, which in the adult 

 are mottled Avith black. Each gland has a layer or capsule of cellular tissue 

 investing it, from which prolongations dip into its substance, forming partitions. 

 The lymphatic and lacteal vessels pass through these bodies in their passage to 

 the thoracic and lymphatic ducts. A lymphatic or lacteal vessel, previous to 



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