A hollow bony structure on the ventral, posterior portion of the skull of placental mammals that encloses parts of the middle and inner ear. In most species, it is formed by the tympanic part of the temporal bone.
Comment:
[development-note] "may be formed from entotympanic and ectotympanic"; [taxon-note] "In extant primates, the structure is found in tarsiers, lemurs, and lorises[WP]. When present in marsupials, it usually forms the alisphenoid; in placentals variously constructed of ectotympanic, entotympanic, petrosal, or a combination of these and others" xsd:string {source="Rose"}