Anatomy of pulmonary vein–associated collecting lymphatics. The cleared lung from Prox1-eGFP mouse was immunostained for GFP and α-smooth muscle actin. Upper images are 3D maximum intensity projections of a whole lung lobe, with detailed expansion showing the region exposed for intravital imaging. The lower image is a single z-slice that shows lymphatics adjacent to the superficial pulmonary vein. Images are representative of cleared lungs of n = 4 mice.