Chandrasekhar, Chaya. Pāla-Period Buddha Images: their hands, hand gestures, and hand-held attributes. PhD Dissertation, Ohio State University, 2004. xvi+375 pp. [official site / PDF (779.3 MB)]
From the Abstract
This study identifies and classifies the Buddha images of the Pāla period (ca. eighth-twelfth centuries) of eastern India and Bangladesh. Specifically, the study examines the number of hands—whether a single pair or multiple pairs—hand gestures, and hand-held attributes of the Buddha images, and analyzes these elements in relation to the essential teachings of Mahāyāna and Vajrayāna Buddhism. […]
About 963 Buddha images among the known Pāla artistic corpus serve as the primary documents for the study.