Air enters the nasal cavity of the respiratory system through the __(1)__. The nasal cavity is divided by the midline __(2)__. The nasal cavity mucosa has several functions. It's major functions are to __(3)__, __(4)__, and __(5)__ the incoming air. Mucous membrane-lined cavities called __(6)__ are found in several bones surrounding the nasal cavities. They make the skull less heavy and probably act as resonance chambers for __(7)__. The passageway common to the digestive system and respiratory systems, the __(8)__, is often referred to as the throat; it connects the nasal cavity with the __(9)__ below. Clusters of lymphatic tissue, __(10)__, are part of the defensive system of the body. Reinforcement of the trachea with __(11)__ rings prevents its collapse during __(12)__ changes that occur during breathing. The fact that the rings are incomplete postieriorly allows food to bukge __(13)__ during its transport to the stomach. The larynx or voice box is built from many cartilages, but the largest is the __(14)__ cartilage. Within the larynx are the __(15)__, which vibrate with exhaled air and allow an individual to __(16)__.