The osteotomy starts at the piriform aperture cranial to the anterior nasal spine and passes through the facial maxillary sinus wall, the zygomaticoalveolar crest, and the maxillary tuberosity to the dorsal surface of the maxillary sinus, separates the caudal tip of the pterygoid process of the sphenoid bone, bends forward to the nasal cavity, runs through the lateral nasal wall in its basal portion, and from there returns to the piriform aperture.
Source: wiktionary