The External Nose
The moist bare skin around the nostrils, the nasal plate, is divided by a median philtrum that continues ventrally to groove the upper lip (see Fig. 4.1). The nasal plate is covered with a thick keratinized epidermis.
In cats its surface is made up of fine tubercles, but in dogs it is made of irregularly formed plaques and sulci that create a pattern that is believed to be individual and therefore available as a means of identification (nose printing). The nasal plate of dogs has no glands of its own and is kept moist by an overflow of the secretion of glands of the nasal cavity (pp. 139 and 140).A curved alar cartilage supports the roof and the wing of the nose. The floor is strengthened by a small accessory nasal cartilage. The wing, the thickened dorsolateral portion of the nostril, is the most mobile part. The nostrils of dogs are comma-shaped, with the tail curving laterally beneath the wing. It is suggested that this separation of the wing from the floor of the nostril allows directional scenting (see Fig. 4.1). The alar fold is an extension of the ventral nasal concha, which terminates within the nasal vestibule at a bulbous enlargement fused with the wing of the nostril.
Congenital malformation of the nasal plane is a common finding in brachycephalic dogs and Persian cats. In this condition the cartilage supporting the nostrils is too weak; the resulting collapse of the wings narrows the nostrils, especially during inspiration. This condition can be relieved by surgery, in which parts of the alar folds are removed. The tissue is highly vascular and bleeds profusely when cut.