Also of interest is the tympanic bone, a part of the skull that surrounds the ear drum.
From the sciencedaily.com
The tegmen tympani, the roof of the tympanic cavity, overlaps the suspensory process of the squamosal bone.
From the en.wikipedia.org
Pakicetids could hear under water, using enhanced bone conduction, rather than depending on tympanic membrane like most land mammals.
From the en.wikipedia.org
The squamosal bone lacks a suspensory process contacting the tegmen tympani, the roof the tympanic cavity.
From the en.wikipedia.org
However, pakicetids were able to listen underwater, by using enhanced bone conduction, rather than depending on tympanic membrane like general land mammals.