44 THE SKELETON OF THE CAT. 
folded so as to enclose spaces, the ethmoid cells. In each 
may be distinguished a cranial portion (4), 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 (¢). 
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 lamine of bone which ensheath the ventral margin of the 
lamina perpendicularis (or the cartilaginous plate which con- 
tinues ventrad from this margin) and unite ventrad of it; the 
two thus form a trough open dorsad. - 
Each becomes horizontal near its caudal end and at the 
same time expands. The expanded portion lies ventrad of the 
labyrinth of the ethmoid, closing in some of its cells: its lateral 
angles are united with the labyrinths. 
At its caudal end the bone articulates with the body of the 
