The study investigates the specialized junctions between endothelial cells in initial lymphatics, which play a crucial role in fluid and cell entry. Unlike conventional continuous zipper-like junctions found in collecting lymphatics and blood vessels, initial lymphatics have discontinuous button-like junctions. These buttons, composed of vascular endothelial cadherin (VE-cadherin) and tight junction-associated proteins, are anchored on the sides of oak leaf-shaped endothelial cells, allowing fluid entry without disrupting junctional integrity. The presence of VE-cadherin is essential for maintaining junctional integrity, while platelet/endothelial cell adhesion molecule-1 (PECAM-1) is not. Growing tips of lymphatic sprouts have continuous zippers, suggesting that buttons are specialized junctions rather than immature ones. Most leukocytes enter the proximal half of initial lymphatics, with the exact entry site influenced by additional factors such as chemokines or adhesion molecules. The findings provide new insights into the mechanisms of fluid and cell entry into lymphatics.The study investigates the specialized junctions between endothelial cells in initial lymphatics, which play a crucial role in fluid and cell entry. Unlike conventional continuous zipper-like junctions found in collecting lymphatics and blood vessels, initial lymphatics have discontinuous button-like junctions. These buttons, composed of vascular endothelial cadherin (VE-cadherin) and tight junction-associated proteins, are anchored on the sides of oak leaf-shaped endothelial cells, allowing fluid entry without disrupting junctional integrity. The presence of VE-cadherin is essential for maintaining junctional integrity, while platelet/endothelial cell adhesion molecule-1 (PECAM-1) is not. Growing tips of lymphatic sprouts have continuous zippers, suggesting that buttons are specialized junctions rather than immature ones. Most leukocytes enter the proximal half of initial lymphatics, with the exact entry site influenced by additional factors such as chemokines or adhesion molecules. The findings provide new insights into the mechanisms of fluid and cell entry into lymphatics.