MR. YOOATT S VETERINARY LECTURES. 
sal passage communicates, and with those of the nasal duct, the 
lachrymal sac, the conjunctiva, the membrane of the pharynx, 
the trachea, the air-cells, the mouth, the tubes of the parotid 
and submaxillary glands, the Eustachian tubes, the tympanum 
of the ear; the oesophagus, the stomach, the intestines, the 
biliary and pancreatic vessels, the urinary and genital pas¬ 
sages. 
The Schneiderian membrane may be considered as presenting 
two surfaces, an adherent and a free one ; the adherent being 
very firm, with difficulty separated from the bone beneath, and 
forming a kind of periosteum to the bone. Lying on this is a re¬ 
ticulated mass of bloodvessels and nerves, particularly on the 
septum, and the sethmoid and superior turbinated bones. There 
is no part of the frame more vascular. On this is the free sur¬ 
face, covered with a mucous fluid to protect it from the painful 
or dangerous influence of the air, the food, or other foreign ob¬ 
jects, and being a kind of factitious integument, particularly be¬ 
neficial in the respiratory passages, subject to the injurious influ¬ 
ence of sudden change of temperature or stimulating gases, and 
in the intestines, defending them from the occasional acrimony of 
some of the ingesta. When this membrane is carefully examined, 
there are numerous minute rounded apertures, irregularly distri¬ 
buted, most plentifully on the lower part of the septum, and on 
the inferior turbinated bone—smaller, and scarcely to be traced on 
the upper part of the septum, or on the sethmoid bone; given 
mostly where there is most exposure to injury. Superiorly it 
is comparatively devoid of mucus, that the olfactory nerves and the 
lateral nasals may ramify with more effect, and be more sensible to 
impression. When the intermediate substance is traced with 
great minuteness, it is found to be glandular; but not composed 
of distinct glands, or even of the smallest granulations, but a 
bed of glandular matter. The natural discharge is limpid, small 
in quantity, and scarcely seen at the nostril. Under inflamma¬ 
tion it becomes increased in quantity, thickened, opaque, and 
even purulent, and that either with or without ulceration. 
In the convolutions of the sethmoid and turbinated bones, and 
in the sinuses of the face and head, the membrane is thinner, 
more delicate in its structure, and the mucous secretion lessened 
in quantity. These parts are out of the reach of danger. No 
current of air blows upon them—no foreign body can injure them; 
and, their function being limited, they have fewer bloodvessels 
and nerves ; the membrane is more easily torn from its attach¬ 
ment, and it possesses comparatively little sensibility. Although 
the function of these sinuses and their membranes is imperfect, it 
seems to be of a double character. The voice is affected by the 
