Fig. 4

Three-dimensional computed tomographic reconstruction of a canine skull. The arrows represent the airways, with the pink arrow showing the common airflow and the red and blue arrows showing the olfactory and respiratory airflow, respectively. The nostrils, the olfactory and respiratory epithelium as well as the olfactory bulb, and the tracheal tube are labeled. During inhalation the air flows from the nares and the nasal vestibule to the maxilloturbinates, then into the ethmoturbinates and the paranasal sinuses towards the pharynx [122]. There is a major difference between breathing and sniffing in dogs. While breathing, most of the inspired air flows through the nasopharynx into the lungs but only a small percentage (12–13%) reaches the olfactory areas [59]. The sniffing process generates external (outside the nostrils) and internal (within the nasal cavity) fluid dynamics. The ambient air is inhaled from the front and exhaled to the side for efficient odorant sampling, whereas each nostril samples separately. A sniff is the first critical step of the olfactory process with the function of generating unique unidirectional laminar airflow patterns to transport environmental odorants into the nasal cavity to the olfactory epithelium [122]. Furthermore, sniffing increases odour sensitivity and affects the intensity of odorants [60, 90]