Some small vessels may lack this layer. Large Elastic Arteries 2. Medium-sized Veins 3. Anchoring filaments extend from outer surface into surrounding CT to hold vessels open - Lymph vessels with valves to prevent backflow in amniotes. Lymph movement is facilitated by skeletal muscle contraction.
Lymph hearts propel lymph in amphibians and to a lesser extent in reptiles.
Also present are phagocytic reticular cells and singular adipose cells. It is not completely known.