See Sun Di, Ti'en Lung Shan Grottoes: Research on the Overseas Stone Statues, Beijing, 2004, p. 133, no. 141, for an illustration of the statues of the north wall of Cave 16, amongst which is a standing monk to the proper right of the seated Buddha, which appears to have closely related features, and which may in fact be the source of the present lot. Other monks with similar features are illustrated ibid., p. 134, no. 144, p. 136, no. 148, and p. 138, no. 152, providing details of the north, east and west walls of the same cave, strongly suggesting that this head may have come from Cave 16 at Tianlongshan.