In the rabbit, mouth breathing is ineffective. They are nasal breathers. The respiratory system comprises nasal passage——->pharynx———–>larynx——–> trachea————–>bronchi———–>lungs.
First, the air comes into the nasal passage. The nasal passage contains nasal bone on dorsal side and palate on the ventral side. The nasal passage opens into internal nares where pharynx is present. The pharynx is the common organ between digestive and respiratory system. Pharynx opens into the larynx, which is also known as the sound box. This organ is responsible for sound production. Larynx ends into trachea also known as windpipe. The windpipe takes all respired air to the lungs, present in the thoracic cavity. It is important to note that thoracic cavity is small in rabbit, in comparison to the digestive system. So, the rabbit can never stay in a way that abdominal contents come into the chest. If this happens, then rabbit will have difficulty in breathing.
Trachea branches into 2 bronchi, namely left and right bronchi. Left bronchi open in the left lung and right bronchi open into the right lung. Further bronchi divide into thinner bronchioles inside the lungs, which further open up in the alveoli. The alveoli are the site of gaseous exchange between external airs with the blood. Bronchi, bronchioles, and alveoli are present inside the lungs. The lungs are a soft mass of tissue lying in the pleural cavity. Lungs are further divided into lobes.