We will look at the the paranasal sinuses.

Sinuses
Video Tour	Rotateable picture
Nasal Sinus From lab book P 169 and 170. Four (paired) paranasal sinuses are air filled spaces within 4 of the bones that border the nasal cavity. Similar to the cavity, they are lined with pseudostratified epithelial that produces a mucus that aids in conditioning (warming and moistening) air. The mucus also aids in defense by entrapping bacteria. The frontal sinus is within the frontal bone posterior to the superior orbital margin and drains through a duct located below the middle nasal concha. The ethmoid sinus is composed of "air cells" within the lateral walls of the ethmoid bone where they drain inferior to the superior and medial nasal concha. These cells can be viewed from the lateral view of this model The sphenoid sinus is located in the body of the sphenoid bone just under the sella turcica. Occasionally the posterior air cells of the ethmoid sinus will open into the sphenoid sinus as well. The frontal and sphenoid sinuses can be observed in most of the mid sagittal models. In the model on the previous page, the superior and middle nasal concha have been removed to expose the ethmoid sinus. The maxillary sinus can be viewed best from a frontal or lateral view. The lateral view has the maxillary sinus. It is the largest of the 4 (paired) sinuses and it sits superior to the alveolar process and inferior to the orbital surface. It drains into the nasal cavity near the middle nasal concha. During a sinus infection, a thick mucus is produced that has to defy gravity to reach the opening. As a result, the sinus does not drain if the head is erect and pressure builds up within the sinus.