Ultrastructural evidence for the mitotic division of neurons in the anterior horn of the fetal rabbit in the later stages of gestation.

Two mitotic cells found in the ventral horn of the fetal rabbit spinal cord at 26 and 28 days post-conception are described. Both are large cells with a much more extensive cytoplasm than is usual during mitosis. The cytoplasm of both cells contained an extensive dilated vesicular structure which was identified as the endoplasmic reticulum. Ribosomes were not present on its surface. The 26 days post-conception cell had an axosomatic synapse on its perikaryon and serial ultrathin sections of the 28 days post-conception cell showed a number of dendrite-like processes arising from its perikaryon and a myelinated axon approaching the pole of the cell opposite the plane of cleavage. These two cells were structurally different from mitotic cells previously described in the central nervous system and appear to be neurons that are at least partially differentiated.