200 
A. LIAUTARD. 
of these two, the one corresponding to the vomer is the widest ; the 
thinnest part is at the union of the anterior and middle third. 
Let us see now the mucous membrane of the nasal cavities, the 
pituitary , or Schneiderian membrane, as it is also named. It covers all 
the organs spoken of, is continued to the skin at the anterior, and with 
the pharyngeal mucous membrane at the posterior opening. Alter cov¬ 
ering the median septum, it reflexes itself into the meatus, lays upon the 
turbinated bones, lines their internal cavities, and surrounds, omboth 
surfaces, their spiral frame ; it even runs through the opening of the 
middle meatus, and lines the cavities of the sinuses. But in passing 
fiom one of these parts to another it undergoes important changes which 
we must know. 
The mucous membrane of the perpendicular septum is thin all over. 
It is the thickest in the whole extent of the inferior extremity, where 
numerous mucous glands are found, with their orifices easily seen with 
the naked eye. Round the anterior and posterior borders, and near the 
inferior extremity, the mucous is much thinner, and shows plainly 
through its transparency the magnificent venous plexus underneath. 
It is undoubtedly upon the cartilaginous portion of the turbinated 
bones that the pituitary membrane possesses its greatest thickness; it may, 
indeed, be about three or four millimeters; there, however, we find the 
same disposition as upon the perpendicular septum, the nearer the pos¬ 
terior chamber of the cavities the thinner it gets ; specially is it so upon the 
superior turbinated ; that of the inferior, looking towards the floor of 
the fossae has always a greater thickness. 
The supeiior and middle meatus have a mucous membrane which 
is so thm that it has been sometimes taken for the periosteum. 
In the inferior meatus, the membrane has about the same thickness 
as that of the inferior extremity of the turbinated ones. Its mobility is 
quite well marked. 
The ophthalmic and nasal arteries carry the blood to the nasal cav¬ 
ities. The veins are more important than these blood-vessels ; they 
possess numerous anastomoses and are without valves—a fact which 
allow of their injection through a large venous trunk—and which can 
be easily seen on a longitudinal section of the head, as there always re¬ 
mains a certain quantity of blood in the plexus which may be pushed in 
all directions by pressure of the finger. . 
Upon the median cartilaginous septum the veins form a handsome 
median network, composed of large trunks almost parallel, anastomosed 
and superposed in three, four or five layers, towards which converge 
