[Fig. 31].—Ethmoid and Vomer, Side View.
![[Fig. 31]](#3418956513767812439_illo043alg.jpg.id-3873195082948362918.wrap-0.html.html){kind=link}
[Fig. 32].—Ethmoid and Vomer, Ventral View.
![[Fig. 32]](#3418956513767812439_illo043blg.jpg.id-9221397534919355867.wrap-0.html.html){kind=link}
a, vomer; b, vertical cells of the labyrinth of the ethmoid; c, horizontal cell of the same; d, part of the ethmoid that forms the lamina papyracea; e, edge of cribriform plate.
The labyrinths ([Figs. 31] and [32]) are attached to the cranial face of the lamina cribrosa, one on each side of the lamina perpendicularis. Each is made of thin bony plates irregularly folded so as to enclose spaces, the ethmoid cells. In each may be distinguished a cranial portion (b), in which the cells are nearly vertical, and a caudal portion (c), in which the cells are nearly horizontal.
The medial surfaces are separated by a space from the lamina perpendicularis. This space is broadest along the junction of the horizontal and vertical portions of the labyrinth. There are thus formed two passageways which correspond to the superior meati of human anatomy.
The lateral surfaces come into contact with the frontal process of the maxillary and the orbital plate of the frontal bone. On the lateral surface of each labyrinth there is a thin irregular lamina of bone lying in a dorsoventral longitudinal plane and closing in some of the ethmoid cells laterally (d). A small part of this lamina, situated near the caudoventral angle of the bone, appears in the orbital fossa on the external surface of the skull between the presphenoid, palatine, and frontal bones or between the lachrymal, palatine, and frontal bones. Sometimes in the entire skull two such pieces may be seen, one in each of these positions. This corresponds to the lamina papyracea of human anatomy.
The dorsocaudal angle of each bone is received into the space between the orbital plate of the frontal and the vertical lamina of the medial border of the frontal. Its ventrocaudal angle is received between the cranial extensions of the lateral walls of the presphenoid, while its ventral surface is overlaid caudally by the expanded portion of the vomer, to which it is attached at its caudolateral angles.
Vomer
([Figs. 31] and [32], a).—The vomer consists of two thin laminæ of bone which ensheath the ventral margin of the lamina perpendicularis (or the cartilaginous plate which continues ventrad from this margin) and unite ventrad of it; the two thus form a trough open dorsad.