What keeps lymph moving through the lymphatic vessels toward the heart?

1. A major difference between the lymphatic and cardiovascular systems is that lymph is not actively pumped by the heart. 2. It is forced through the vessels by the movements of the body, the contraction of skeletal muscles and breathing. 3. One-way semi-lunar valves in the lymphatic vessels stop backflow, so all of that squeezing moves lymph toward the heart. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 21 "The Lymphatic and Immune System", section 21.1 Anatomy of the Lymphatic and Immune Systems_