ANATOMY OF REGIONS. 
199 
in the frontal and ethmoid bone—the former is wider than the second, 
which terminates into a very acute angle. 
The floor , wider but shorter, has for bas‘e the incisive process of the 
small maxillary bone, the reflexed portion of the great maxillary and the 
palate ; it forms the posterior wall of the inferior meatus. Altogether, 
in front of it, one will find the entrance of the canal of Jacobson, and 
the inferior opening of the lachrymal canal, pierced on the boundaries 
of the nostrils and nasal cavities. 
Posterior Chamber of the Nasal Cavities .—Behind the posterior 
border of the naso pharyngeal opening, there is an elongated diver¬ 
ticulum, some five centimeters in length,* and situated between the in¬ 
ternal plate of the frontal, the cribriform sheet of the ethmoid and the 
sphenoid. This space is filled by the ethmoidal volutes and the supe¬ 
rior extremity of the anterior turbinated bone—the volutes are formed 
of bony sheets rolled upon themselves, and covered by the nasal 
mucous membrane. They are attached above upon the cribiform plate, 
their inferior extremity ends into cul de sac folded outwards to implant 
themselves upon the external plate of the bone. 
Between the lateral masses of the ethmoid and the bony walls sur¬ 
rounding, there are narrow spaces where a somewhat considerable quan¬ 
tity of thick mucosities are always found. 
Let us now consider the septum which separates the two nasal cavi¬ 
ties. It is nothing else but the perpendicular lamella of the ethmoid, 
continued forward by a more or less ossified cartilage ; almost always 
do we find a nucleus of ossification at the inferior and anterior part, on 
a level with the apex of the nasal bones. This nucleus, already wide in 
adults, extends with age, as often in old individuals, it unites above to 
the plate of the ethmoid, and thus is the septum almost entirely bony. 
The posterior border of the septum is rounded and implanted in the 
fissure of the vomer ; the anterior rests upon the suture of the nasal 
bones ; it expands on each side under these bones, which it separates 
from the mucous membrane of the roof. Its anterior extremity supports 
the cartilages of the nostrils. The faces are flat and form the internal 
walls of each nasal cavity; they present specially above a number of 
furrows for the divisions of the rich venous plexus of the mucous mem¬ 
brane. 
The thickness of the perpendicular septum Varies much ; the me¬ 
dian portion is always thinner than the anterior and posterior borders ; 
* Two inches, 
