The cytogenesis and radial migration of cranial nerve efferent neurons in the developing brain stem of the bovine.

The cytogenesis of motor neurons of the immature brain stem of the bovine has been examined by light-and electron microscopy from the periods of origin and migration of the motor neurons until their transformation into relatively mature neurons in their area of destination. Up to 2.7 cm CRL intensive cell migration occurs from the ventromedial cell column in a ventrolateral direction, leading to the formation of the definitive viscero-efferent nucleus of the facial nerve. Electron-optically these cells exhibit features of immature neurons which are extending leading processes in the direction of their destination. At 2.5 cm CRL a formation of vertical cell columns can be identified in the facial nucleus which has reached its final position. Its perikaryon areas come into contact with radial fibres. This morphological pattern marks the process of migration. An increased ultrastructural differentiation is typical for neurons which are localized in their ultimate position.