Abstract
This project presents the osteological connections of the petrosal bone of the extant Hippopotamidae Hippopotamus amphibius and Choeropsis liberiensis by a virtual osteological dissection of the ear region. The petrosal, the bulla, the sinuses and the major morphological features surrounding the petrosal bone are labelled, both in situ and in exploded models presenting disassembly views. The directional underwater hearing mode of Hippopotamidae is discussed based on the new observations.