The paranasal sinuses are a former term that is now referred to as the sinuses. The nasal parts are the external nose, the nasal cavity, and the sinuses, and the sinuses are one of the three parts. The sinuses are divided into four groups of eight, which are the bilateral maxillary sinuses, bilateral septal sinuses, bilateral frontal sinuses and bilateral pterygoid sinuses. The sinuses are symmetrical from side to side, with the bilateral maxillary sinuses on either side of the external nose and the largest group of sinuses below the orbits. The septal sinuses are between the eyes and on the deep side of the nasal bridge. The frontal sinuses are in the forehead, above the orbits. The pterygoid sinuses are located deeper, below the pterygoid saddle, above the posterior nostril, and behind the nasal septum. The maxillary sinus opens in the middle nasal tract; the anterior group of septal sinuses opens in the middle nasal tract; the posterior group of septal sinuses opens in the upper nasal tract; the frontal sinus opens in the middle nasal tract; and the pterygoid sinus opens in the pterygoid sieve crypt.