In the vertebrate embryo, a rhombomere is a transiently divided segment of the developing neural tube, within the hindbrain region (a neuromere) in the area that will eventually become the rhombencephalon. The rhombomeres appear as a series of slightly constricted swellings in the neural tube, caudal to the cephalic flexure. In human embryonic development, the rhombomeres are present by day 29. Function In the early developmental stages of the neural tube, segmentation of the neuroepithelium occurs. This segmentation turns into a series of neuromeres. Each segment is called a rhombomere. Every rhombomere develops its own set of ganglia and nerves. Later on in development, rhombomeres form the rhombocephalon, which forms the hindbrain in vertebrates. Each rhombomere expresses its own unique set of genes, which has been shown to influence postnatal rhythmic behaviors, such as respiration, mastication, and walking. In mice, it was shown that the patterning of the neural tube into rhombomeric segments may regulate spatial and temporal appearance of the central pattern generator. Rhombomeres are considered self-governing developmental units, with certain aspects of the rhombomere phenotype being determined at the time of formation. Each rhombomere expresses a unique combination of transcription factors, and so each rhombomeric domain has its own distinct molecular cues that could, theoretically, establish rhombomere-specific patterns of neuronal differentiation. Some of these neuronal populations have been identified in some species. Many of the mature hindbrain nuclei can occupy either one or several rhombomere-derived regions. Vestibular nuclei have been shown to span all the rhombomeres, some correlating with the boundaries of the rhombomeres. Using phosphorylated retrograde labeling, it has been shown that vestibulospinal groups correspond mostly to single rhombomeres rather than over several rhombomeric regions. It has also been shown that the vestibule-ocular groups can either relate to single or multiple rhombomeres, as long as the rhombomeres are closely related. The conclusion drawn was that segmentation of the hindbrain contributes to the way axons project within the vestibular complex. Finally, vestibulospinal neurons have been shown to differentiate in three neighboring rhombomeres, specifically r4, r5, and r6. While vestibule-ocular neurons differentiate across seven, the least differentiated in f4. The method of this differentiate is still unknown, with many types of proteins involved in both the migration, expression of proteins, and for neuron growth and apoptosis. The types of receptors, as well, can vary their activity to be cell-specific. Rhombomeres determine the pattern of the following maturation of the