Otic vesicle chick, invagination of the otic placode occurs passively due to the movements of the surrounding placode. The otic placode in zebrafish, on the other hand, occurs by cavitation; the ectodermal placode condenses and forms an ovoid ball directly below the embryo surface. Otic vesicle formation occurs later, during the 25-30 somite stage in mice. Otic vesicle Otic vesicle, or auditory vesicle, consists of either of the two sac-like invaginations formed and subsequently closed off during embryonic development. It is part of the neural ectoderm, which will develop into the membranous labyrinth of the inner ear. This labyrinth is a continuous
Otic notch Otic notch Otic notches are invaginations in the posterior margin of the skull roof, one behind each orbit. Such notches are found in labyrinthodonts and some of their immediate ancestors, but not in their reptilian descendants. The presence or absence of the otic notches is one of the traits used to separate the amniotes from the amphibian grade tetrapods. The notches have been interpreted as part of an auditory structure and are often reconstructed as holding a tympanum similar to those seen in modern anurans. Analysis of the "columella" (the stapes in amphibians and reptiles) of labyrinthodonts however indicates that