Comparing the nasal cavity to a longer corridor, the sinuses are the rooms around the corridor, some over the corridor, some on either side of the corridor, some in front, some behind, each with windows opening into the corridor, known as the sinuses. The sinuses are cavities within the bones surrounding the nasal cavity, which are the frontal sinus, pterygoid sinus, maxillary sinus and septal sinus, the four of which make up the sinuses. The frontal sinus is located deep in the arch of the eyebrow, the butterfly sinus is located at the base of the skull, and the maxillary sinus is located from the inferior orbital wall up to the alveolar process, all opening into the nasal cavity. Since the opening of the maxillary sinus is upward, the maxillary sinus often causes inflammation and affects the surrounding adjacent nerves, the skull, and the eye, leading to complications.