Tibetan saddlescan be high art, covered with ornate metalwork and inlaid jewels. This one, given to National Geographic Explorer Joseph Rock about a century ago by a lama warlord named Xiang Cicheng Zhaba, is on the humbler side. But it was no less a treasure to Rock, an ethnographer and botanist with a taste for finery. In 1924, he became the first American to visit Muli, Xiang’s isolated mountain kingdom.