126 OSTEOLOGY. 
walls of the ethmoidal cells. Curving downwards, backwards, and a little out- 
wards from the roof of the fore part of this meatus is the uncinate process (pro- 
cessus uncinatus). This bridges across the irregular opening on the inner wall of 
the maxillary sinus, and articu- 
lates inferiorly with the eth- 
moidal process of the inferior 
turbinated bone. The hinder 
extremity of the middle turbin- 
ated bone articulates with the 
ethmoidal crest on the vertical 
ee See plate of palate bone. Sat 
lar plate The cribriform plate (lamina 
eribrosa) is the horizontal 
lamina which connects the 
lateral masses with the vertical 
—Uncinate process Plate, much in the same manner 
as the cross limb of a capital T 
Hachrymal process ig arranged. (lt. occwplesiule 
interval between the orbital 
plates of the frontal bone, 
De hee roofing in the nasal fossee in- 
Crista galli 
Os planum 
Middle / 
turbinated 
bone 
3 turbinated bone feriorly, and superiorly forming 
Maxillary process Ethmoidal process on either side of the erista galli 
Fig, 98.—SHOWING ARTICULATION oF INFERIOR TurBINATED bWO shallow olfactory grooves 1n 
Bone with EraMorp. which, in the recent condition, 
the olfactory lobes of the cere- 
brum are lodged. Numerous foramina for the transmission of the olfactory nerves 
pierce this part of the bone—those to the inner and outer sides of the groove 
are the largest and most regular in their 
arrangement. Along the outer edges of the 
eribriform plate two notches can usually be 
distinguished; when articulated with the 
frontal bone these form the inner openings of 
the ethmoidal canals. Leading forward from 
the anterior of these there is often a groove 
which crosses to the side of the crista galli, 
where it ends in a slit, which allows of the 
transmission of the nasal nerve to the nose. 
Posteriorly the cribriform plate articulates 
with the ethmoidal spine of the sphenoid. 
Vertical plate 
/ Alar process 
prt for nasal nerve 
/Infundibulum 
Ethmoidal 
7 cells 
Ethmoidal 
/ Srooves 
Connexions.—The ethmoid articulates with the 
sphenoid and sphenoidal turbinals, the frontal, the 
two nasals, two superior maxillee, two lachrymals, 
two inferior turbinals, two palates, and the vomer. 
Variations.—The size of the os planum is liable 
to considerable variations. In the lower races it tends 
to be narrower from above downwards than in the 
higher, in this respect resembling the condition met Fic. 99.—ETHMOID AS SEEN FROM ABOVE. 
with in the anthropoids. The os planum may fail to 
articulate with the lachrymal owing to the union of the frontal with the orbital process of the 
superior maxilla in front of it. (Orbito-maxillary frontal suture. A. Thomson, Journ. Anat. 
and Physiol., vol. xxiv. p. 349.) Division of the os planum by a vertical suture into an anterior 
and posterior part has been frequently recorded. The number of the turbinals may be increased 
from two to four, or may be reduced to one. (Report of Committee of Collect. Invest. Journ. 
Anat. and Physiol., vol. xxviii. p. 74.) 
Os planum 
Cribriform plate Lateral mass 
Ossification takes place in the cartilage of the nasal capsule. Each lateral mass has 
one centre, which appears about the fourth or fifth month in the neighbourhood of the 
os planum. From this the laminze around the ethmoidal air cells are formed which are 
complete at birth, the air sinuses in this instance not being formed by the absorption 
of cancellous bone. From these centres the turbinals are also developed, and these, too, 
are ossified at the ninth month. 
