Its arc-shaped design and the guiding lines enable an excellent trace of the osteotomy line. Lateral and transversal osteotomies may be realized through an endonasal intervention. The guiding lines prevent the chisel from slipping off the osteotomy line Applicable from both sides, left and right hand side. The round prominent projections of the guides are well felt through the skin. The surgeon may always control the position of the chisel.