Charles Hose,
The Pagan Tribes of Borneo
“ In all the tribes of this group the social organisation is in the main similar, and this affinity is borne out by their material culture, thus they may be regarded as originally one people. Tribes calling themselves Bahau now live along the Mahakam above Mujub and include one Kayan group; on the upper Rejang are Bahau tribes under the name of Kayan, and a small section has advanced into the Kapuas area and settled on the Mendalam which again includes Kayans and kindred tribes. ”
