The eye and the nasal accessory sinuses are intimately related; in fact, the bony walls of the orbit are formed chiefly by the walls of the sinuses. The upper wall is formed largely by the floor of the frontal sinus, while the inner wall is formed principally by the lateral wall of the ethmoid cells, and the floor of the orbit by the roof of the maxillary sinus.
The bony walls are very thin, varying from 1 to 12 mm. in thickness. Aside from being at times of tissue-paper thinness, they may be defective; that is, they may have dehiscences. These dehiscences allow the mucous membrane of the sinuses to come in direct contact with the orbital tissues or the optic nerve. The dehiscences may be due to senile atrophy or to formative anomalies. Zuckerkandel reports fourteen and Onodi eighteen cases of congenital dehiscences of the paper plate of the ethmoid. These openings