most dorsal group of neurons originated from rhombomere 1, and the posterior raphe—which forms from the rhombomeres—is believed to derive from the posterior rhombomeres at a slightly later stage of embryonic development. Rhombomeres also lead to the creation of vestibular projection neurons, which are probably produced relatively early in the developmental stages of the brain stem. In the rhombomeres, members of the T-box transcription factor family, have been linked to the proper development of migrating cells. While the hindbrain is developing, trigeminal cell bodies have been shown to migrate dorsolaterally within rhombomeres 2 and 3, while facial cells move dorsolaterally into r5 near the pial surface. Neurons that form the facial nucleus are produced in r4, but move along the anteroposterior axis of the hindbrain into r6, after which they move dorsolaterally. The vestibuloacoustic neurons are also produced in r4. However, they have a unique migration pattern, where their cell bodies cross the midline to the contralateral side. From this one can conclude that multiple subclasses of motor neurons are produced in specific locations in the developing hindbrain. All of them are related by the expression of Tbx20. Motor neurons produced in the hindbrain have Tbx20 selectively expressed. In Tbx20 mutations, the patterning of the regions of the rhombomeres and motor neurons were normal when they were conditional mutations and the neurons were post-mitotic. Tbx20 mutants pre-mitotic showed many cell migration deficiencies, including abnormal dorsolateral migration of the trigeminal cells, arrested tangential migration of the facial neurons, and a lack of transmedian migration of vestibuloacoustic cells. However, hindbrain motor neurons lacking Tbx20 retained the ability to extend neurites into the periphery. The complete elimination of Tbx20 does not cause trigeminal and facial neurons to switch to hypoglossal neurons. Facial neurons have been shown to migrate tangentially from r4 to r6, while trigeminal neurons that are produced in r2 migrate dorsolaterally non-radially. Vestibuloacoustic cells migrate along the midline at r4 contralaterally in the hindbrain. Tbx20 seems to have context-dependent transcriptional activity. This means that it is able to control different cell migration programs specific to different types of cells. It must be able to regulate these patterns by different means. While many studies have been done on rhombomeres where rhombomeres are grafted cross species, imprecision can occur. One possible source is damage to the rhombomere during the removal, transportation, or grafting process. Another possible source is the mixture of the cells