The anatomy of the middle ear region of the skull is described for the families of the Avian orders Pelecaniformes and Ciconiiformes. Emphasis is placed on the foramina and paths of the nerves and blood vessels. The morphology of the basicranium and quadrate is also discussed. Comparative analyses of the characters are used to assess taxonomic conclusions. Extant Pelecaniformes consist of six families, four of which are monogenic: Phaethontidae, Pelecanidae, Anhingidae and Fregatidae; one is composed of two genera: Sulidae; and the last has three genera: Phalacrocoracidae. Several years ago a relationship was suggested which would ally the Phaethontidae and the Fregatidae. While these families share several non middle ear characters the anatomy of the middle ear is not compatible with any particular relationship. Indeed, several obvious differences are described. The data presented here are consistent with the idea that the Phaethontidae and the Fregatidae each form a separate group of Pelecaniform birds, with the rest of the families forming a third group. Several differences in the middle ear region of the species of Anhingidae suggest that the family may be composed of two genera. While sharing many Ciconiiform characters the Ciconiidae have been shown not to be as closely related to the Ardeidae as they are to other families of Ciconiiformes. In addition, evidence is presented to support the recent idea that the three species of ibis (I. ibis, I. cinereus and I. leucocephalus) be united within the genus Mycteria. Also supported is the notion that Balaeniceps is Pelecaniform in character, and not Ciconiiform.

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Much emphasis has been placed on the middle ear region of reptiles and mammals as a taxonomic character. However, the anatomy of the middle ear region of birds has yet to be described adequately. The literature on the middle ear of birds is reviewed briefly and then the osteology and soft anatomy of the middle ear region of the skull are described for the families of the avian order Procellariiformes. Particular emphasis is paid to the foramina and paths of the nerves and blood vessels. Also discussed is the morphology of the basicranium and the quadrate. Comparative analyses of the characters are used to assess taxonomic conclusions.

The morphology of the middle ear region including the basicranium and quadrate of tinamous is compared among ratites and flying birds belonging to the Procellariiformes, Sphenisciformes, Pelecaniformes, and Ciconiiforms. The middle ears of tinamous and ratites share a number of important characters including absence of a separate foramen for the glossopharyngeal nerve; eustachian tube, carotid artery, and stapedial artery encased in bone; and a metotic process with vascular canals or notches. Outgroup analysis confirms these characters as synapomorphies. These data support the position that the Tinami and Ratiti form a monophyletic assemblage.

The morphology of the middle ear region including the basicranium and quadrate ofSfncchio is very siiidiii. io tlir saiiic region in the orders Procellariiformes. Pelecaniformes. Ciconiiformes and Sphenixifomies. Strufhio though, has some unique middle ear characters such as the lack ofa chorda tympani nerve, the arrangement of the glossopharyngeal and vagus nerve foramina, the structure in the upper neck of the external ophthalmic vein and the position of the Eustachian tube. The articulatory surfaces for the quadrate both on the zygomatic process of the squamosal and the mandible are unique in Strut& when compared to the several orders mentioned above.