aia e 
THE ETHMOID BONE. 125 
short and shallow grooves leading to the foramina which pierce the cribriform plate ; 
these are for the lodgment of the olfactory nerves. 
The lateral mass or labyrinth (labyrinthus) is composed of papery bone, 
enclosing a large number of air cells; these are arranged in three groups, an 
anterior, a middle, and 
a posterior, the walls of 
which have been broken Anterior and posterior 
. : ethmoidal grooves 
in front, above, behind, 
and below, in the pro- 
cess of disarticulation. 
Externally they are _ 
closed in by a thin ob- (pita Surtnee) 
long lamina, the orbital 
plate or os planum 
(lamina papyracea), 
which forms a part of Middle meatus- 
the inner wall of the 
orbit, and articulates 
above with the orbital 
plate of the frontal, Fic. 96.—ETHMOID AS SEEN FROM THE RIGHT SIDE. 
which here roofs in the 
ethmoidal cells. The line of this suture is pierced by two canals, the anterior and 
posterior ethmoidal canals, both of which transmit small ethmoidal vessels, whilst 
the anterior also gives passage to the nasal nerve. Jn front the os planum articu- 
lates with the lachrymal bone; whilst below, by its union with the orbital surface 
of the superior maxillary bone, the air sinuses in both situations are completed. 
Posteriorly the os planum articulates with the sphenoid, and at its posterior 
inferior angle for a variable distance with the orbital process of the palate bone, 
both of which serve to close in the air cells. The mesial aspect of the lateral mass 
displays the convoluted turbinated processes, usually two in number, though 
occasionally there may be three—rarely more. In cases where there are two 
ethmo-turbinals they are separated posteriorly by a deep groove. A channel is 
thus formed in the back part of the lateral and upper aspect of the nasal fossz, 
called the superior meatus, which is roofed in by the superior turbinated process 
(concha superior), whilst its floor is formed by the upper surface of the middle 
turbinated process (concha media). The posterior ethmoidal cells open into this 
ncn lAvtetior cmoiann aeatus. in frontiof the’ superior meatus, 
plate groove which only grooves the posterior halt of 
Sih [X this aspect of the bone, the surface is 
= PP rounded from above downwards and before 
backwards, and forms the inner wall of 
the anterior and middle ethmoidal cells. 
tunning obliquely from above downwards, 
and backwards over the mesial surface of 
the superior concha, are a number of fine 
grooves continuous above with the fora- 
mina in the cribriform plate; these are 
; Timeiioen roses fewer and more scattered in front, do not 
Crista galli 
Alar process 
Infundibulum 
Anterior 
ethmoidal 
cells 
Vertical plate 
Middle turbinated bone Unciform process 
Superior 
turbinated bone 
Snperior 
meatus 
Inferior 
turbinated 
bone 
| Bee eee nee aaine Nasa Asreon or. bass'on to the middle concha, and are for 
a Lert Lareran Mass oF ErHMorD. the olfactory nerves. 
‘ The middle turbinated process (concha 
media) is nearly twice the length of the superior. Its anterior extremity is united 
for a short distance to the superior turbinated crest on the inner side of the 
frontal process of the superior maxilla. By its thickened free convoluted border 
‘it overhangs a deep groove which runs along the under surface of the lateral mass. 
This is the middle meatus of the nose. It receives the openings of the middle 
ethmoidal cells and a passage which runs upwards and forwards from it, the 
infundibulum. This communicates with the anterior ethmoidal cells and the 
frontal sinus. The outer side of the middle meatus is formed by the thin inner 
‘ 
