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A2,A3: Otocyst, otic capsule, rhombencephalon and rhombomeres.
DEVELOPMENT OF THE NERVOUS SYSTEM
Al-7: Midbrain and hindbrain. The isthmus can be observed on A3-4 as a constriction between the mid- and hind-brain. The hindbrain is already subdivided into two parts, the slim myelencephalon and the wider metencephalon. The boundary between these two parts is roughly at the level of the otic vesicles A3-4.
Development of the Auditory System
A3: Otocyst; surrounding mesenchyme = otic capsule. Note proximity of otocyst to wall of rhombencephalon. Superior glossopharyngealganglion. Vestibulo-cochlear-facial ganglion complex (R). Trigeminal ganglion.
