5B is a side view of the structure of FIG. 25A; [0042]FIG. 25C is a perspective view of the structure of FIG. 25A; and [0043]FIG. 26A is side view of a cavity forming device carrying an expandable structure of the type shown in FIGS. 23 and 24A to 24C; [0044]FIG. 26B is a perspective view of the distal end of the cavity forming device shown in FIG. 26A, showing the assembly of the proximal end of