Wyverns: though dragons are not physically described (and why would they be, everyone knows what a dragon looks like), the wyvern is described. We are told they are relatives of Dragons, but they are smaller and have but two legs. We may infer from this dragons have more than two legs. The AD&D Monster Manual would later depict dragons with four legs and a pair of wings, wyverns with two legs and a pair of wings.
Dragons: the description for this iconic monsters includes excellent rules for subduing a dragon (p. 12). In this manner a player could acquire a dragon NPC hireling. Some referees would extend these rules to other types of monsters.
Demon Illustration, Bottom of Page: in the current printing the winged humanoid is not labeled. Before the cease and desist letter from the Tolkien Estate there was a caption: Balrog.