Figure 4. Porcine retinal arteriovenous crossings. Images from serial paraffin sections of porcine retinal arteriovenous crossing sites stained with trichrome. The artery has a much thicker wall (stained blue) and a rounded shape in cross sections as compared to the vein. A–D: The artery is crossing above the vein. E–H: The vein is crossing above the artery. Large vessels are clearly above the inner retinal level in B, D, and H.