from
The Collaborative International Dictionary of English v.0.48
Petrosal \Pe*tro"sal\, a. [See {Petrous}.] (Anat.)
(a) Hard; stony; petrous; as, the petrosal bone; petrosal
part of the temporal bone.
(b) Of, pertaining to, or in the region of, the petrous, or
petrosal, bone, or the corresponding part of the temporal
bone.
[1913 Webster]
{Petrosal bone} (Anat.), a bone corresponding to the petrous
portion of the temporal bone of man; or one forming more
or less of the periotic capsule.
[1913 Webster]