THE SKULL. 43 
a transverse perforated plate, the cribriform plate (lamina 
cribrosa), attached to the caudal end of the lamina perpendicu- 
laris and the labyrinths. 
The lamina perpendicularis (Fig. 43, ; Fig. 42, p) is a 
flat four-sided bone. By its caudal margin it is continuous with 
the cribriform plate; by its ventral margin it is enclosed by the 
halves of the vomer; by its dorsal margin it unites with the 
crest formed by the vertical portion of the nasal bone craniad 
and with the vertical lamina of the medial margin of the frontal 
caudad, while its cranial margin is continued into the septal 
cartilage of the nose. Its lateral faces are smooth and free. 
The lamina cribrosa or cribriform plate (Fig. 42, 0) is 
elongated heart-shaped, with the apex of the heart ventrad. 
Its caudal face is concave and looks into the cranial cavity. 
It presents three irregular longitudinal rows of holes, one 
median and two lateral, for the passage of the olfactory fibres 
from the cranial cavity into the nasal cavity. Its cranial face 
is continuous along the medial line with the lamina perpendic- 
ularis, and at the sides with the labyrinths. 
The notch in the heart is directed dorsad and receives the 
vertical lamina of the medial border of the frontal bone. The 
Fic, 31 —ETHMOID AND VOMER, Fic. 32.—ETHMOID AND VoMER, 
SIDE VIEW. VENTRAL VIEW. 
a, vomer; 4, vertical cells of the labyrinth of the ethmoid; ¢, horizontal cell of 
the same; d@, part of the ethmoid that forms the lamina papyracea; e, edge of cribri- 
form plate. 
apex of the heart articulates with the cranial end of the dorsal 
surface of the presphenoid. Its lateral margins are articulated 
with the ethmoidal ridges on the medial surface of the frontal 
bone. 
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 
