There is a great deal of individual variation in the size and shape of the maxillary sinus, and generally men have larger sinuses than have women, in accordance with the overall larger and cruder bony facial skeleton typical of the male.

Judging the shape of the sinus by its capacity is as misleading as predicting the shape of a container by the amount it holds. In some people, the sinus may be a fairly smoothly contoured cavern. In others, the sinus is partially partitioned by incomplete bony septa. Again, it is important to note that in the same individual the sinus of one maxilla may vary in shape and size from its bilateral counterpart. Therefore, it is precarious to draw conclusions about the morphology of both sinuses by examining only one. Each sinus must be carefully evaluated as an individual unit and as part of a functional whole.

The shape of the maxillary sinus has been described as pyramidal. The base of the pyramid (5) forms the lower wall of the nasal septum, and its apex (6) is directed toward the zygomatic arch. One wall of the pyramid faces superiorly, the orbital cavity (7) ; one posteriorly (8), toward the infratemporal fossa; one anteriorly (9), toward the face; and one inferiorly (1), toward the dental arch and palate. Naturally, a sinus is not an architecturally precise pyramid, with straight walls and sharp angles. The walls curve to accommodate other cranial structures and slope to join one another.

In a young adult with normal dentition in good occlusion, the lowest part of the sinus (11) usually lies superior to the first molar and the second premolar. This lowest part, formed by the junction

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