32 
MR. YOUATT’S VETERINARY LECTURES, 
DELIVERED AT THE UNIVERSITY OF LONDON. 
LECTURE IV. 
The Nostrils and the Schneiderian Membrane. 
The Nostrils. — The nasal cavity on either side gradually di¬ 
minishes anteriorly, and at length terminates in an irregular ovoid 
orifice on either side. The triangular spaces between the nasal 
and anterior maxillary bones are filled up by elastic cellular sub¬ 
stance and integument, and which are supported by these bones, 
and by two cartilages on each side. The face gradually dimi¬ 
nishes towards the lower part. The broad muzzle of the ox 
would be an unsightly termination of the face of the horse ; in 
consequence of this, the external nostrils are correspondingly 
small, and they seem barely large enough for the purpose of quiet 
and undisturbed breathing:. But we often exact from the horse 
a great and a cruel exertion of speed, accompanied by a corres¬ 
ponding expenditure of animal power, and this demanding an 
equivalent supply of arterial blood, and that to be obtained only 
by a proportional admission of air into the lungs. 
The apparently contracted nostril of the horse would not admit 
of sufficient air to arterialize the blood, and support the rapidly- 
exhausted contractility of the over-worked muscular fibre, were 
there not a beautiful apparatus of soft distensible parts, and car¬ 
tilage and muscle, occasionally to expand the nostril, and admit 
the increased quantity of air which the animal may demand. 
Attached to the soft parts composing the nostril, are several pow¬ 
erful muscles, which serve to expand these orifices; and there are 
two cartilages on each side, which, while they admit of the ex¬ 
pansion of the nostrils, restore them again to their natural dimen¬ 
sions by their inherent elasticity. The cartilages are attached to 
and supported by the points of the nasal bones. There are two 
larger ones superiorly, and two smaller and lunated ones below. 
They give form to the nostril in the natural state of breathing, and 
likewise in the act of increased respiration, and, the muscular 
power which dilated them ceasing to act, they bring the nostrils 
back to their original dimension and form. 
The Muscles of the Nostrils. —The principal muscles concerned 
in expanding the nostrils are the transversales (dilatatores nasi 
anteriores ), that can scarcely be said to have any proper origin, 
for they are bound down on the point of the nose, and are inserted 
into each of the cartilages. When they act, they^draw these 
