chap. XL] THE LYMPHATIC VESSELS. 85 



exceedingly thin connective tissue membrane with a 

 few elastic fibres. The valves are semi-lunar folds of 

 the endothelium and intima. 



111. The lymphatics in the tissues and organs 

 form rich plexuses. They are tubular vessels, the wall 

 of which is, like that of a capillary blood-vessel, 

 a single layer of endothelial plates (Fig. 52). The 

 lymphatic is often many times wider than a blood 

 capillary. The endothelial plates are elongated, but 



Fig. 52. Lymphatic Vessels of the Diaphragm of the Dog, stained with 

 Nitrate of Silver. 



The endothelium forming the wall of the lymphatics is well shown ; , valves. 



(Atlas.) 



not so long as in a blood capillary, with more or less 

 sinuous outlines, but this depends on the amount of 

 shrinking of the tissue in which the vessel is embedded ; 

 when there is no shrinking in the tissue or in the vessel, 

 the outlines of the cells are more or less straight. 



The lymphatics are supported by the fibrous con- 

 nective tissue of the surrounding tissue, which does 

 not, however, form part of their wall. 



