This is from the second episode not the first, but the Legendary Pokémon Ash sees on the wall are (in order from top left, to top right, to bottom left, to bottom right):
Moltres, Articuno, Zapdos and Arcanine.
In the first episode he sees ho-oh flying in the sky,while in the secondin the poke center he sees zapdos,articuno,moltresand arcanine carved on stone while he is talking with prof.oak