(1038–1227). Tangut is recorded in a Chinese-inspired logographic script, whose interpretation presents many difficulties, even though multilingual dictionaries have been found. Gong Hwang-cherng has compared Old Chinese, Tibetic, Burmese and Tangut in an effort to establish sound correspondences between those languages. He found that Tibetic and Burmese correspond to two Old Chinese vowels, *a and *ə. While this has been considered evidence for a separate Tibeto-Burman subgroup, Hill (2014) finds that Burmese has distinct correspondences for Old Chinese rhymes -ay : *-aj and -i : *-əj, and hence argues that the development *ə > *a occurred independently in Tibetan and Burmese. Fieldwork The descriptions of non-literary languages used by Shafer and Benedict were often produced by missionaries and colonial administrators of varying linguistic skill. Most of the smaller Sino-Tibetan languages are spoken in inaccessible mountainous areas, many of which are politically or militarily sensitive and thus closed to investigators. Until the 1980s, the best-studied areas were Nepal and northern Thailand. In the 1980s and 1990s, new surveys were published from the Himalayas and southwestern China. Of particular interest was the discovery of a new branch of the family, the Qiangic languages of western Sichuan and adjacent areas. Distribution Most of the current spread of Sino-Tibetan languages is the result of historical expansions of the three groups with the most speakers – Chinese, Burmese and Tibetic – replacing an unknown number of earlier languages. These groups also have the longest literary traditions of the family. The remaining languages are spoken in mountainous areas, along the southern slopes of the Himalayas, the Southeast Asian Massif and the eastern edge of the Tibetan Plateau. Contemporary languages The branch with the largest number of speakers by far is the Sinitic languages, with 1.3 billion speakers, most of whom live in the eastern half of China. The first records of Chinese are oracle bone inscriptions from c. 1250 BC, when Old Chinese was spoken around the middle reaches of the Yellow River. Chinese has since expanded throughout China, forming a family whose diversity has been compared with the Romance languages. Diversity is greater in the rugged terrain of southeast China than in the North China Plain. Burmese is the national language of Myanmar, and the first language of some 33 million people. Burmese speakers first entered the northern Irrawaddy basin from what is now western Yunnan in the early ninth century, in conjunction with an