I actually didn't have a problem solving this one. Make the obvious assumption that it's symmetrical (including R15), and that it's a very simplistic skull and cross bones (cross bones are linked together), and you can finish it no problem. The skull is 100% symmetrical, the cross bones are not. Here's the solution for the cross bones:
R10: C3-C4, C18
R11: C4, C17
R12: C3-C5, C16-C18
R13: C6-C7, C14-C15
R14: C8-C9, C12-C13
R15: C10-C11
R16: C8-C9, C11-C12
R17: C4-C12, C13-C14, C17-C18
R18: C3, C6, C15-C16.