Identifying named landmarks on the coffin bone shows two clear features: the extensor process and the semi lunar crest. The extensor process is a projection on the dorsal surface where the distal extensor tendon attaches, giving the tendon a point of leverage over the bone. The semi lunar crest is a curved ridge near the proximal edge that helps define the articular area with the joint above and with the navicular region, making it a distinct, recognizable feature of P3. These two parts are specific and commonly cited as key landmarks on the coffin bone. The other options point to structures not on the coffin bone. The navicular tubercle is on the navicular bone, not P3. The proximal phalanx border belongs to the bone above (P2). The solar margin is a part of P3 too, but the extensor process and semi lunar crest are the most distinct, well-defined features used to describe P3 in anatomical references.