Anatomy of the Dog’s Nose

The dog has two nostrils (nares) divided by a cartilaginous and bony septum. The tip of the dog’s nose – rhinarium – is typically moist and cool to touch. When a dog flares its nostrils to sniff, the shape of the nostril openings change thus allowing redirection of air into the upper part of the snout and more direct airflow to the olfactory area. The slit at the side of the nares is used in the expiration of breath during sniffing.

Humans have up to 5 million scent receptors, whereas the dog has up to 300 million.

This is possible because a dogs long nose contains a labyrinth of thin bones called turbinates, which are all lined by an epithelium. This provides a very large surface area for the air breathed to pass over. In the anterior part of the nose, the bones are known as maxilla-turbinates and they are lined by a respiratory type epithelium producing mucus. 

It is in the posterior part of the nose  containing ethmoid turbinates that the lining epithelium is olfactory in type and this contains the 300 million olfactory receptors, or neurones, needed to recognise the odour molecules. The neurones need maximum contact with the air containing the odour molecules and therefore have hair-like projections – or cilia. In mammals it is thought that each olfactory receptor cell only expresses one single odorant receptor gene 3.

Once the odour is recognised, a pathway of tiny nerves relay signals to the brain area dedicated to olfaction – the olfactory lobe – which then interprets the odours in combination with other specialised areas of the brain. As part of the olfactory anatomy there is a basal plate of bone known as the Lamina Transversa (not seen in humans) which creates an olfactory shelf or recess separated from the respiratory section. This allows odours to accumulate and be held for recognition even while air is exhaled. Lining the olfactory shelf are cilia; minuscule hair-like structures found on olfactory receptor cells and enhance the detection of odour molecules. 

The complexity of the labyrinth of thin turbinate bones in the nose is best seen in cross section. Below are two views of the anterior opening of the nostril in a dog’s skull showing the maxillo-turbinates, which would be covered by respiratory type epithelium.

Nature can mimic and help explain the structure of the nose.

The first image depicts the olfactory shelf lined by ‘cilia’ in a Foxglove. The second depicts ‘cilia’ with attached ‘mucous droplets containing odour molecules’, depicted in a bed of moss. 

Dogs have a separate ‘sense of smell site’ for social contact

It consists of two elongated fluid-filled sacs above the roof of the mouth. It is named the VOMERONASAL ORGAN or JACOBSON’S ORGAN – and it detects body scents (pheromones – hormone-like substances) allowing sexual and social assessment of other dogs.

The Dog’s Nose    The importance of mucus  

  Sniffing   Volatiles