Many leaves have a big, obvious vein that runs along their center, and many veins emerge from

Question:

Many leaves have a big, obvious vein that runs along their center, and many veins emerge from it. What is the large vein called (and can a leaf have more than one [look at Figure 6-2])? The smaller veins that emerge from it? What are the very smallest veins of a leaf called? Which veins supply water directly to mesophyll cells—the biggest veins or the smallest?

Figure 6-2