The Cut Mesh command enables you to cut or divide a mesh selecting the triangles directly on the mesh.
Select the mesh you would like to cut.
To reset the mesh selection, right-click on Mesh in the selection list, choose the Reset option in the context menu and then select the mesh again.
Select the area you want to delete or separate from the mesh; select the Selection through box to select all the triangles in the area, by default only the visible triangles will be selected.
In the Cut Mesh selection list, select the Split check box to split the mesh into parts instead or removing the selected area.
Click the OK button to confirm the operation and exit the procedure, or the Apply button to apply the operation, or the Cancel button to abort.