Biomedical Ephemera, or: A Frog for Your Boils

Metallic cast of the combined pneumatic cavities of the face

a. inferior nasal fossa b. median nasal fossa c. superior nasal fossa d. sphenoidal sinus e. internal carotid artery f. sheath of the optic nerve g.  antrum of Highmore (maxillary sinus) h. infundibulum (ethmoidal infundibulum) i. nasolacrymal canal k. ethmoidal cells l. frontal sinus

Much of the frontal skull consists of pneumatic (air-filled) cavities. Many of these are known as sinuses.

While the function of our sinuses is not fully understood, they’re known to effect the filtration of inhaled air, and decrease the weight of our skull.

Atlas and Text-Book of Dentistry including Diseases of the Mouth. Gustav Preiswerk, 1909.

Frontal Sinus and Nasal Duct

While adults with sinus problems are all too familiar with the frontal sinuses, they're not structures that we're born with!

The maxillary and ethmoid sinuses are present from birth, but the sphenoid and frontal sinuses only form after the frontal bone begins to ossify ("turn to bone" - when we're born it's largely tough membrane, to allow passage through the birth canal), around age 2.

The frontal sinuses are largely formed by age 9, but don't reach their full size until puberty. When fully formed, they are part of the primary immune defenses, producing mucous to trap germs and filter air from the nose.

Interestingly, over 5% of people don't form frontal sinuses. The absence of frontal sinuses does not appear to present significant hindrance to the immune abilities of the body. However, chronically dry nose is a frequent side-effect.

Atlas of Applied Topographical Human Anatomy for Students and Practitioners. Translated to English by J. Howell Evans, 1906.

Nasal Accessory Sinuses

I had a question regarding the location of the ethmoid sinus the other day. This is one of the better diagrammatic skulls that I've seen that displays their position in relation to the face. On the inside edge of the orbit, the cells that have been laid bare are the ethmoidal air cells. The ethmoid sinus isn't one single cavity within the skull, but several sets of air cells within the ethmoid bone, behind the nasal cavity. 

Diseases of the Nose and Throat. Herbert Tilley, 1919.

Partial Cross-Section of Adult Skull

Displaying the divisions of the ear and naso-pharyngeal cavity. As you can see, even though the skull has some pretty well-defined zones and areas, everything is a lot more inter-connected than most of us learn about in grade school. The close connection between the ear canal and throat is why, when you have a sore throat, many times earaches come along with it, and why when you have a sinus headache, the ears often feel "plugged up". 

A Practical Treatise on the Diseases of the Ear Including a Sketch of Aural Anatomy and Physiology. D. B. St. John Roosa, 1884.