LYMPHATIC VESSELS 227 



capillaries, form anastomosing meshes in all tissues where blood capil- 

 laries are found. They are most abundant in the perivascular connective 

 tissues, where they form a dense plexus about the wall of the blood-ves- 

 sels. 



The wall of the lymphatic capillary, like that of the blood capillary, 



FIG. 235. SUBCUTANEOUS LYMPHATIC VESSEL OF A FETAL PIG. 



At the right is a small blood-vessel. Hematein and eosin. Highly magnified. 

 (After MacCallum.) 



consists of a single layer of endothelium. This endothelium probably 

 forms a complete lining for the lymphatic capillary and is continuous 

 through larger and larger vessels with that of the veins, from which, 

 according to Sabin (Amer. Jour. Anat., 1902), the lymphatics are 

 originally developed. 



The relation of the lymphatic capillaries to the tissue spaces is not 

 as yet definitely settled. It was formerly thought that these spaces were 



