1) Fistular 2) Fistulous 3) Hollow 1) Fistular 2) Hollow 
• (v. t. & i.) To make hollow or become hollow like a fistula, or pipe.
Fis'tu·late transitive verb & i. [ Confer Latin fistulatus furnished with pipes.] To make hollow or become hollow like a fistula, or pipe. [ Obsolete] 'A fistulated ulcer.' Fuller. 
fistulate 1. To make hollow or become hollow like a fistula, or pipe. 2. Like a reed or tube. 3. Containing tubes or tube-like parts.