Thank you for writing to us.
There are splitters between Pane Left 1, Pane Left 2, Pane Left 3 (see the attachment).
You can place multiple RadSplitContainers in a RadSplitContainer. To make the Container vertical you should use its Orientation property and set it to Vertical in the main RadSplitContainer.
If we missed something do not hesitate to contact us again.
the Telerik team