I - Respiratory System of the Rat

The respiratory system consists of two lungs and the passages by which their internal cavities are connected to the exterior. Starting anteriorly, these cavities include: the nasal cavities, which are separated from one another by the nasal septum and from the buccal cavity by the palate.
The pharynx is divided into the naso-pharynx above the palate, and the oro-pharynx behind the buccal cavity. The edge of the soft palate acts as a valve to prevent food from passing into the naso-pharynx and then into the nasal cavities during swallowing. The opening from the pharynx into the larynx, or voice box, is called the glottis. As mentioned previously, the glottis is closed over, during swallowing of food, with a gate-like epiglottis, to prevent the passage of food into the larynx and lower respiratory passages.

Examine the rat thoracic cavity

Note where the trachea divides posteriorly to form two main branches or primary bronchi (singular bronchus), each of which enters a lung. Both the trachea and bronchi have cartilaginous rings embedded in their walls to prevent collapse. As they enter the lungs, each bronchus divides into secondary branches or bronchial tubes as it enters the lung.

Note the left pleural cavity with the single lobe of the left lung and the heart lying in its covering, the pericardium. Note that the lungs each lie in a cavity lined by a thin membrane, the parietal pleural; the pleura from both lungs meet in the midline to form a mediastinal septum.