Pin (chess) Pin (chess) In chess, a pin is a situation brought on by an attacking piece in which a defending piece cannot move without exposing a more valuable defending piece on its other side to capture by the attacking piece. Moving the attacking piece to bring on the pin is called pinning; the defending piece so restricted is described as pinned. Only pieces that can move an indefinite number of squares in a horizontal, vertical, or diagonal line (i.e. bishops, rooks, and queens) can pin. Kings, knights, and pawns cannot pin. Any piece can be pinned except the king, since the
Evolution of the horse horse", "Orohippus" was not a true horse and did not live in the mountains. It resembled "Eohippus" in size, but had a slimmer body, an elongated head, slimmer forelimbs, and longer hind legs, all of which are characteristics of a good jumper. Although "Orohippus" was still pad-footed, the vestigial outer toes of "Eohippus" were not present in "Orohippus"; there were four toes on each fore leg, and three on each hind leg. The most dramatic change between "Eohippus" and "Orohippus" was in the teeth: the first of the premolar teeth were dwarfed, the last premolar shifted in shape and function