1. 1 Objectives of this Study The vertebrate middle ear has attracted the interest of morphologists for more than a century. Its difficult structure, its complicated evolutionary derivation, and its integration of branchial, cranial, and otic materials into a single func tional unit have made it a key organ for the understanding of vertebrate structures and their evolutionary history. Gaupp's (1898, 1913) and Reichert's (1837) comparative morphological studies of the vertebrate middle ear repre sented milestones for anatomy in the general recognition and acceptance of Darwin's theory of evolution. These fundamental studies notwithstanding, today's knowledge of avian middle ear structures is still characterized by descriptive studies focusing on character sampling to elucidate high-level phylogeny. Phylogenetic studies have considered either structural aspects of the bony stapes exclusively (Feduccia 1974, 1975a,b, 1976, 1977, 1978), or focused on the anatomy of the middle ear cavity, neglecting the sound trans mission apparatus (Saiff 1974, 1976, 1978a,b, 1981, 1982, 1983, 1988). Other studies have investigated late-stage embryos and concentrated on the develop ment of the skull, considering middle ear structures only as a side aspect. However, there are considerable structural differences between the middle ears of late-stage embryos, hatchlings, and adults of the same species. Although vertebrate morphology requires a meticulous knowledge of comparative middle ear data and calls upon an elaborate system of homologies, it turns out that knowledge of middle ear structural details is widely dispersed among different species and different developmental stages, making a comparison even more difficult.

Inhalt
1 Introduction.- 1.1 Objectives of this Study.- 1.2 Literature Review.- 1.3 Theoretical Concepts: Questions and Answers.- 1.4 Basic Functional Concepts of the Avian Middle Ear: The Transfer Function.- 1.5 Evolutionary History of Middle Ear Structures.- 2 Materials and Methods.- 2.1 Species List.- 2.2 Macroscopic Dissections.- 2.3 X-Ray Computed Tomography.- 2.4 Morphometry.- 2.5 Microscopic Investigations.- 2.6 Nomenclature, Synonyms, and Abbreviations.- 3 Results.- 3.1 Species Biology.- 3.2 External Ear Opening: Position, Ear Covers, Form, and Width of Opening.- 3.3 External Auditory Meatus (Meatus acusticus externus): Position and Course, Bordering Structures, and Relation to Fascia and Muscles.- 3.4 Osteology of the Tympanic Region.- 3.5 Tympanic membrane (Membrana tympanica): Position, Orientation, Fixation, and Histology.- 3.6 Tympanic Recesses and Pneumatization of the Neurocranium.- 3.7 Siphonium and Pneumatization of the Mandible and the Quadrate Bone.- 3.8 Pharyngotympanic Tube.- 3.9 Arthrology of the Quadrate Bone.- 3.10 Columella: Stapes and Extracolumella.- 3.11 Ligaments of the Middle Ear.- 3.12 Muscles of the Middle Ear.- 3.13 Nerves.- 3.14 Paratympanic Organ.- 3.15 Arteries.- 4 Discussion.- 4.1 Towards a Functional Analysis of the Avian Middle Ear.- 4.2 Phylogenetic Implications.- 5 Summary.- 6 References.- 7 Subject Index.- 8 List of Abbreviations and Synonyms Used in Avian Middle Ear Studies.