expansion of ethmoid sinuses into frontal bone, and the other develops from invagination. They never coalesce so drain independently. Function Respiration The nose is the first organ of the upper respiratory tract in the respiratory system. Its main respiratory function is the supply and conditioning, by warming, moisturising and filtering of particulates of inhaled air. Nasal hair in the nostrils traps large particles preventing their entry into the lungs. The three positioned nasal conchae in each cavity provide four grooves as air passages, along which the air is circulated and moved to the nasopharynx. The internal structures and cavities, including the conchae and paranasal sinuses form an integrated system for the conditioning of the air breathed in through the nose. This functioning also includes the major role of the nasal mucosa, and the resulting conditioning of the air before it reaches the lungs is important in maintaining the internal environment and proper functioning of the lungs. The turbulence created by the conchae and meatuses optimises the warming, moistening, and filtering of the mucosa. A major protective role is thereby provided by these structures of the upper respiratory tract, in the passage of air to the more delicate structures of the lower respiratory tract. Sneezing is an important protective reflex action initiated by irritation of the nasal mucosa to expel unwanted particles through the mouth and nose. Photic sneezing is a reflex brought on by different stimuli such as bright lights. The nose is also able to provide sense information as to the temperature of the air being breathed. Variations in shape of the nose have been hypothesised to possibly be adaptive to regional differences in temperature and humidity, though they may also have been driven by other factors such as sexual selection. Sense of smell The nose also plays the major part in the olfactory system. It contains an area of specialised cells, olfactory receptor neurons responsible for the sense of smell (olfaction). Olfactory mucosa in the upper nasal cavity, contains a type of nasal gland called olfactory glands or Bowman's glands which help in olfaction. The nasal conchae also help in olfaction function, by directing air-flow to the olfactory region. Speech Speech is produced with pressure from the lungs. This can be modified using airflow through the nose in a process called nasalisation. This involves the lowering of the soft palate to produce nasal vowels and consonants by allowing