[1] The upper surface of the labyrinth presents a number of half-broken cells, the walls of which are completed, in the articulated skull, by the edges of the ethmoidal notch of the frontal bone.

The posterior surface presents large irregular cellular cavities, which are closed in by articulation with the sphenoidal concha and orbital process of palatine bone.

[1] In front of the lamina papyracea are some broken air cells which are overlapped and completed by the lacrimal bone and the frontal process of the maxilla.

It consists of a thin lamella, which descends from the under surface of the cribriform plate, and ends below in a free, convoluted margin, the middle nasal concha.

It is rough, and marked above by numerous grooves, directed nearly vertically downward from the cribriform plate; they lodge branches of the olfactory nerves, which are distributed to the mucous membrane covering the superior nasal concha.