The Dog’s Nose

All mammals possess five sense: TOUCH, HEARING, TASTE, SIGHT AND SMELL.
The majority of humans use sight as their main sense to assess the world around them, the smell sense is subsidiary and the human nose is unlikely to be able to smell cancers. 
In the dog the sense of smelling, the olfactory system, is the main special sense and it is extremely sensitive and efficient. Possibly 30% of a dogs brain is dedicated to analysing odour. It is estimated that the percentage of a dog’s brain devoted to analysing odours is 40 times larger than that of a human1.
Dogs can detect odour diluted at 1-2 parts per trillion – this is the equivalent of a teaspoon of sugar in a million gallons of water; two Olympic-sized swimming pools2. 
The structure of the dog’s nose is important. The nose is formed by bones, muscles and soft tissue and includes a blood supply of arteries and veins plus nerves, which are connected to specialised areas in the brain.

The combined functioning of these tissues is shown in this video of a Labrador showing the constant movement involved in sniffing. Note how the dog wriggles its nostrils, which it can do separately, and opens and closes the slit at the side of the nostril. 

The Dog’s Nose   Anatomy   The importance of mucus  

  Sniffing   Volatiles