xiv THE LYMPH 507 



and lung, right side of thorax, and heart, and part of the upper 

 surface of the liver, unite in the right lymphatic trunk ; all the 

 other lymph vessels, including those which come from the intestines 

 (known as lacteals, because during the absorption of the digestive 

 products of alimentation they conduct the chyle, which has a milky 

 aspect), lead into the thoracic duct. 



In this union of the lymphatics into ever-widening channels, 

 their diameter does not increase as rapidly as that of the veins 

 moreover, they often form plexuses which anastomose among 

 themselves ; while, lastly, they enter all along their course into 

 special relations with the so-called lymphatic glands which, from 

 a schematic point of view, may be considered as analogous in 

 structure to the rete mirabile of the blood-vessels, and which retard 

 the flow of the lymph along the vessels that conduct it. 



(&) The lymph capillaries are simpler in structure than the 

 lymphatic vessels properly so-called. They consist of a simple 

 membranous coat, the exceedingly delicate structure of which, 

 when stained with silver 

 nitrate, shows flat plates 

 with characteristic wavy 

 outlines interlacing one 

 with another (Fig. 239). 

 They have no valves, but 

 are usually larger in 

 calibre than the smallest 



Of the lymphatics, and FIG. 239. Epithelioid platelets of lymphatic capillaries 



distinctly larger than ( ^ v 5!f t>8 int " stine> treated with silver nitrate ' 

 the blood capillaries. 



They are irregular in form, and anastomose among 'themselves so 

 as to form a species of network, with uneven meshes and verv 

 varied form. This lymphatic rete, irregularly excavated from the 

 connective tissue which supports it, opens or communicates freely 

 with the lymph vessels, which, although smaller than the 

 capillaries, have a more regular course, are clothed with fusiform 

 epithelial cells of less sinuous outline, and are provided with 

 valves. 



To form a clear conception of the difference in form, arrange- 

 ment, and proportions of the blood and the lymphatic capillary 

 network, Fig. 240, in which the two capillary retes are injected 

 with contrasting stains, may be studied. 



From the physiological point of view it is important to note 

 the special relation of the lymphatics and the blood-vessels in 

 particular parts of the body, e.g. the central nervous system, the 

 parenchyma of the liver, the bone tissues. In these regions the 

 smallest arterial and venous blood-vessels are enveloped with 

 lymphatic sheaths, just as the heart is invested by the pericardium 

 and the viscera by the peritoneum (perivascular lymphatics, Fig. 



