This study identifies specialized junctions between endothelial cells of initial lymphatics, termed "buttons," which facilitate fluid and cell entry into lymphatic vessels. These buttons are discontinuous, button-like junctions that differ from the continuous zipper-like junctions found in collecting lymphatics and blood vessels. Buttons are composed of vascular endothelial cadherin (VE-cadherin) and tight junction-associated proteins, including occludin, claudin-5, zonula occludens-1, junctional adhesion molecule-A, and endothelial cell-selective adhesion molecule. VE-cadherin is essential for maintaining junctional integrity, while platelet/endothelial cell adhesion molecule-1 is not. Buttons are found in the initial segment of lymphatics, where fluid enters, while zippers are present in the distal segment. Buttons allow fluid to enter without disrupting junctional integrity, as they are not fully formed junctions. Leukocytes primarily enter the proximal half of initial lymphatics. The study suggests that buttons are specialized junctions rather than immature ones, and that fluid and leukocyte entry occur at different sites. The findings highlight the importance of specialized junctions in lymphatic function and provide new insights into the mechanisms of fluid and cell entry into lymphatic vessels.This study identifies specialized junctions between endothelial cells of initial lymphatics, termed "buttons," which facilitate fluid and cell entry into lymphatic vessels. These buttons are discontinuous, button-like junctions that differ from the continuous zipper-like junctions found in collecting lymphatics and blood vessels. Buttons are composed of vascular endothelial cadherin (VE-cadherin) and tight junction-associated proteins, including occludin, claudin-5, zonula occludens-1, junctional adhesion molecule-A, and endothelial cell-selective adhesion molecule. VE-cadherin is essential for maintaining junctional integrity, while platelet/endothelial cell adhesion molecule-1 is not. Buttons are found in the initial segment of lymphatics, where fluid enters, while zippers are present in the distal segment. Buttons allow fluid to enter without disrupting junctional integrity, as they are not fully formed junctions. Leukocytes primarily enter the proximal half of initial lymphatics. The study suggests that buttons are specialized junctions rather than immature ones, and that fluid and leukocyte entry occur at different sites. The findings highlight the importance of specialized junctions in lymphatic function and provide new insights into the mechanisms of fluid and cell entry into lymphatic vessels.