An arrow points from a box labeled “head” to a two-tiered box at right. The tiers contain the text “12” and “?”, respectively. Below this box, a two-tiered box contains the number “15” in the top tier; an arrow points from the bottom tier to another two-tiered box below. The tiers in this box contain the text “3” and “NULL”, respectively. Together, the bottom two boxes are labeled “Lost nodes.”