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The tribes with which we in Burma are most intimately concerned form, so to speak, a central stream which moved down south from the primæval breeding ground, between the Tibetans on the one hand and the Lolos on the other. Whatever may have been the point from which they started, it is certain that they must have at one period penetrated into the valleys near the headwaters of the Mekong and Salween, and for some distance in the far north their course must have spread over all the country in the neighbourhood of these two rivers. Now, we know that at about the 30th parallel of latitude there rises out of the maze of unexplored hills to the west of the Salween what Mr. G. Litton (one of the few persons who has so far seen it) describes as a "crescent of mountains" which forms the watershed between the Salween and the Brahmaputra, from the southern edge of which spring the sister streams, the N'maikha and the Malikha, which combine to form the Irrawaddy. We must keep this crescent in mind when we consider the movement of the Tibeto-Burmans from the north, for along a considerable portion of its length it is practically an insuperable barrier, and it is clear that as the Tibeto-Burman tribes came down, some of them were brought up by its snow-clad heights and were obliged, if they wished to pursue their southerly course, either to come out east and follow the Salween southwards or fetch a circuit towards Assam and the Brahmaputra in the west and so reach hill-ridges and fresh valleys along which their way could be pursued. We know this by the present distribution of the Tibeto-Burmans and by the test of language. There are signs of a common ancestry in the not very remote past in the speech of the Burmans, the Lisaws, the Chins and the Kachins, yet there are enough differences between the vernaculars of those of them who must have come down to the east of the crescent and of those who must have come
