| 要旨 |
Parrots have developed novel head structures in their evolutionary history. To better understand the unique evolution of the head in parrots, the developmental pattern of the skull of the budgerigar (Melopsittacus undulatus) was initially described on the basis of transparent skeletal specimens. In spite of a prokinetic skull, the cranio-facial hinge of parrots was formed by secondary transformation of dermal bones. Next, the peculiar skeletal myogenesis in the first visceral arch of parrots was described, mainly focusing on the development of two new jaw muscles. One of the parrot-specific muscles, M. ethmomandibularis, was initially detected at Nymphicus hollandicus stage 28 (N28) as the rostral budding of M. pterygoideus. After N32, the muscle significantly elongates rostrodorsally toward the interorbital septum, following a course lateral to the palatine bone. Another parrot-specific muscle, M. pseudomasseter, was first recognized at N36. The muscle branches off from the posteromedial M. adductor mandibulae externus and grows in a dorsolateral direction, almost covering the lateral surface of the jugal bar. At present, unique patterning of the cephalic neural crest cell migration and the trigeminal nerve branches in parrot embryos is being described with immunostaining.
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