<P> While the human brain is dominated by a large visual cortex, the dog brain is dominated by a large olfactory cortex . Dogs have roughly forty times more smell - sensitive receptors than humans, ranging from about 125 million to nearly 300 million in some dog breeds, such as bloodhounds . This is thought to make its sense of smell up to 40 times more sensitive than human's . These receptors are spread over an area about the size of a pocket handkerchief (compared to 5 million over an area the size of a postage stamp for humans). Dogs' sense of smell also includes the use of the Vomeronasal organ, which is used primarily for social interactions . </P> <P> The dog has mobile nostrils that help it determine the direction of the scent . Unlike humans, the dog does not need to fill up his lungs as he continuously brings the odor into his nose in bursts of 3 - 7 sniffs . The dog's nose has a bony structure inside that humans don't have, which allows the air that has been sniffed to pass over a bony shelf and many odor molecules stick to it . The air above this shelf is not washed out when the dog breathes normally, so the scent molecules accumulate in the nasal chambers and the scent builds with intensity, allowing the dog to detect the faintest of odors . </P> <P> One study into the learning ability of dogs compared to wolves indicated that dogs have a better sense of smell than wolves when locating hidden food, but there has yet been no experimental data to support this view . </P> <P> The wet nose, or rhinarium, is essential for determining the direction of the air current containing the smell . Cold receptors in the skin are sensitive to the cooling of the skin by evaporation of the moisture by air currents . </P>

Where is the trunk located on a dog