Segmental pattern and nuclei in the human embryonic brain at stage 13.

Studies of serial sections and reconstructions of embryos at stage 13 (32) postovulatory days) revealed that the cranial neural tube in the investigated embryos possesses 15 neuromers: 1 telencephalic, 3 diencephalic, 3 mesencephalic, and 8 rhombencephalic. Within the primary efferent column all nuclei of the cranial nerves may be distinguished. Also fibers entering brain from cranial nerve ganglia form the common afferent tract. The relation of neuromers to the motor nuclei of the cranial nerves is following: M1-oculomotor, M2-trochlear, Rh2-trigeminal, Rh4-facial, Rh6-glossopharyngeal, Rh7-vagal, Rh8-hypoglossal.