44 THE SKELETON OF THE CAT. 



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 laminae of bone which ensheath the ventral margin of the 

 lamina perpendicularis (or the cartilaginous plate wiiich 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 



