mouse-split-window-vertically

mouse-split-window-vertically is an interactive compiled Lisp function in `mouse.el'.

It is bound to <vertical-line> <C-mouse-2>, <vertical-scroll-bar> <C-mouse-2>.

(mouse-split-window-vertically CLICK)

Select Emacs window mouse is on, then split it vertically in half.
The window is split at the line clicked on.
This command must be bound to a mouse click.