Split Cell dialog box
Table Tools Layout > Merge > Split Cell
Splits the selected cell(s) in a table into two more cells.
Split into rows
Splits the selected cells horizontally, into rows. The small preview on the right reflects the current selection.
Split into columns
Splits the selected cells vertically, into columns. The small preview on the right reflects the current selection.
Number of rows or columns
Determines the resulting number of rows or columns to which the selected cells should be split. Enter the number of desired rows or columns.