Answer:
open, close
Explanation:
The trachea is cartilaginous tube which connects pharynx and larynx to lungs and thus allowing passage of air.
C-shaped cartilages are open at area where trachea is nearest esophagus, which leads from throat to stomach. It reinforces anterior and lateral sides of trachea to maintain airway open.
The trachealis muscle bridges gap between free ends of the C-shaped cartilages at posterior border of trachea and is adjacent to esophagus. The primary function of trachealis muscle is to constrict trachea, allowing the air to be expelled with more force during coughing.
