The nasal structure protects the entrance to the nose, which directs the inhaled air into a certain course. Through contact with the mucosa the air is tested, cleaned, approximated to body temperature, humidified or dried. To accomplish this the nasal passage must have a minimum size. With partial or complete loss of patency of the nose, the mouth is used vicariously as the air passage. The inhaled air is no longer prepared adequately, since the oral mucosa can not completely take over the function of the nasal mucosa. Obstructed nasal breathing is unhealthy and is considered annoying. In addition it creates a change in the sound of the voice. Even the most ideal shape of external nose can not satisfy the patient if it is purchased with the loss of nasal function. Therefore it is important to observe the physiological principles in rhinoplasty. On the other hand the air-flow conditions in the nose can be improved by external rhinoplasty even without enlargement of the nostrils. — Fig. 14 shows the dependence of the air current conditions on the shape of the external nose. Proetz and Mink, especially, have dealt with the laws concerning the passage of air in the nose.