FIG 3. Sequential, more lateral dissections of the skull and the FSDP (A–F and E') matched to sagittal CT sections of the skull (A'–C' and F').

A, A'. Sagittal structures. The nasal septum is a composite structure, formed by the perpendicular plate of the ethmoid bone anterosuperiorly and by the vomer posteroinferiorly. The inferior margin of the vomer rests upon the nasal crest of the maxillary and palatine bones. The superior margin of the vomer supports the perpendicular plate of the ethmoid bone.

B, B'. Paramedian structures. Removal of the nasal septum reveals the inferior, middle, and superior turbinates. The superior turbinate attaches to the skull base. The middle turbinate shown in B is superimposed (green) onto the sagittal CT (B') to illustrate how the vertical portion of the basal lamella extends to the skull base at the cribriform plate. Its superior border has variable shape.

C, C'. Image C displays a simplified posteromedial oblique view of the middle turbinate and its basal lamella. The basal lamella has three portions. The vertical portion of the basal lamella attaches to the cribriform plate, the middle and posterior portions attach to the lamella papyracea, and the posterior margin of the basal lamella attaches to the perpendicular plate of the palatine bone. Typically, the vertical, middle, and posterior portions of the basal lamella are oriented in near-sagittal, coronal, and horizontal planes, respectively. Usually, the middle and posterior portions appear irregular in shape because of encroachment by adjacent ethmoid air cells. In C, the inferior edge of the middle turbinate and the medial edge of the middle and posterior portions of the basal lamella together have an angular configuration in the sagittal CT (C') that highlights the middle and posterior portions of the basal lamella (green). The basal lamella in C' can be conceptualized by removing the most medial portion of the middle turbinate and the vertical portion of the basal lamella from B'.

Continued

D, Removing the middle turbinate and the vertical portion of the basal lamella exposes, from anterior to posterior, the agger nasi extending to the frontal process of the maxillary bone, the lacrimal bone, the uncinate process of the ethmoid bone extending upward toward the skull base, the hiatus semilunaris (dashed red line), the ethmoid bulla, and the middle and posterior portions of the basal lamella extending laterally toward the lamina papyracea. The hiatus semilunaris is the narrow, slitlike passage between the uncinate process and the ethmoid bulla, through which the ethmoid infundibulum communicates with the middle meatus (6). The ethmoid infundibulum is the space bounded by the uncinate process anteromedially, the ethmoid bulla posterolaterally, and the lamina papyracea anterolaterally (6). Simultaneous removal of the wall of the frontal sinus shows the relationship of the frontal ostium to the superior compartment of the FSDP and how the sinus cavity tapers inferiorly toward the frontal ostium.

E, E'. Removal of the anterior portion of the uncinate process exposes the ethmoid infundibulum. In this specimen, the superior compartment of the FSDP drains directly into the ethmoid infundibulum, which then drains through the hiatus semilunaris to the middle meatus. E' displays a three-dimensional view of the frontal sinus and the superior and inferior compartments of the FSDP (blue).

F, F'. The frontal ostium extends posteriorly from the anterior frontal bone ridge to the posterior wall of the frontal sinus and is oriented nearly perpendicular to the posterior wall of the sinus. The superior compartment of the FSDP lies inferior to the frontal ostium. In this specimen, the inferior compartment of the FSDP is the ethmoid infundibulum. In F', the ethmoid infundibulum is bounded anteriorly by the agger nasi cell and the uncinate process and posteriorly by the ethmoid bulla. The middle and posterior portions of the basal lamella of the middle turbinate (green) separate the anterior and posterior ethmoid air cells (see also Fig 4E, the coronal CT of the same specimen).