Nostril

The nostril is part of the nasal plane; in domestic mammals it takes the form of a more or less wide slit, oblique in a lateral or dorso-caudal direction and convex ventrally. Each nostril is separated on each side of the nose by a furrow, the philtrum. It opens onto the nasal vestibule and corresponds to the entrance to the nasal cavity.

Its ventral edge is made up of a fold of skin incompletely supported by cartilaginous and fibrous formations, concave and close to the upper lip.

Its dorsal edge is formed by the wing of the nose, it is convex, generally thinner and more mobile, stretched by a more or less wide cartilaginous blade belonging to the alar cartilage. It is very short in pigs whose nostrils are almost circular.

The medial corner is always wider and rounded, except in sheep, goats and rabbits, where it is narrow.

The lateral commissure is narrow, except in the pig, and raised a little dorsally, so that the nostril draws a horizontal comma with a lateral-dorsal tail which extends into a furrow, the alar furrow. Barely marked in carnivores and rabbits, absent in pigs, it is broad and clear in ruminants.