ANATOMY OF REGIONS. 
157 
In Sheep, the region is convex in all directions. 
In Dogs , it is more developed inferiorly than superiorly. Its length 
varies in the different breeds, its bony frame does not extend to the 
nose, but for a length of about 1 inch or 1^- inch, the superior border of 
the septum nasi only is felt, thus the inferior portion of the nasal fossa 
has a certain mobility—the whole region is very vascular. 
b. —NOSTRILS. 
These are the external openings of the nasal cavities. In horses, 
because of the length of the soft palate, it is the only way through 
which air can reach the lungs. 
The nostrils are openings, elongated from upwards and downwards, 
and slightly oblique inwards, so as to be nearer to each other towards 
their lower extremity. They have two lips or borders, and two com¬ 
missures. 
The internal border is nearly straight, and is covered superiorly by 
the external lip —this one is strongly convex, and prominent over the 
surrounding parts. The superior commissure is formed by the external 
lip which curves itself inwards, and then forwards so as to cover inter¬ 
nally the internal border. This commissure presents a peculiar diverti¬ 
culum of the nasal cavities, cul de sac, called the false nostril. The 
inferior commissure curves slightly inwards; it presents, at the point of 
union of the skin with the nasal mucous membrane, the orifice of the 
nasal gutter , inferior opening of the lacrymal canal. 
This form of the nostrils, which is that of the animal at rest, is 
considerably modified during locomotion, or in any other state where 
respiration is rendered more active. Then the opening increases special¬ 
ly by the spreading of the internal lip, which becomes very concave, 
and exposes the red internal mucous of the nostrils. 
The skin of this region is strongly adherent to the parties under¬ 
neath. It is covered with abundant short hairs, intermixed with others, 
long, coarse and rough, true organs of feeling. The interior of the 
nostrils is also covered with hairs, stiff, but in smaller number. They 
protect the nostrils from the entrance of dust or foreign bodies, while 
allowing air to penetrate through them. 
When the skin is removed, which requires much care, one finds 
round the nostrils a strong fibro muscular tissue, perforated, here and 
there, by the bulbs of the thick hairs already alluded to. There is but 
one layer of muscular tissue, formed by the terminal fibres of the trans- 
