Morphologische Untersuchungen am Mittelohr der Marsupialial

Morphological studies on the auditory bulla of marsupials The resent study on the comparative anatomy of the marsupial auditory bulla starts with that of the didelphids; ontogenetic data are included. It becomes clear from these comparisons, that the marsupial bulla is throughout composed of the same skeletal elements. Contrary to widespread opinion, there exists no good evidence for the existence of an entotympanic in any marsupial. The tympanic process of the petrosal develops relatively late in ontogeny as ‘additional bone’ (“Zuwachsknochen” of Starck ); the same holds true for the tympanic process of the alisphe-noid. Biometric study of the tymanic ring in didelhids reveals that the tympanic membrane does only slightly increase with skull size (pronounced negative allometry). It is surprising, however, that the data of the tympanic diameter do arrane at two distinct levels of regression. Several taxa of didelphids must have jumped at this level independently. The possible functional meanings of these data are briefly discussed.