sensory fibres of the olfactory nerve into the cranial cavity. Paranasal sinuses The mucosa that lines the nasal cavity extends into its chambers, the paranasal sinuses. The nasal cavity and the paranasal sinuses are referred to as the sinonasal tract or sinonasal region, and its anatomy is recognised as being unique and complex. Four paired paranasal sinuses – the frontal sinus, the sphenoid sinus, the ethmoid sinus and the maxillary sinus drain into regions of the nasal cavity. The sinuses are air-filled extensions of the nasal cavity into the cranial bones. The frontal sinuses are located in the frontal bone; the sphenoidal sinuses in the sphenoid bone; the maxillary sinuses in the maxilla; and the ethmoidal sinuses in the ethmoid bone. A narrow opening called a sinus ostium from each of the paranasal sinuses allows drainage into the nasal cavity. The maxillary sinus is the largest of the sinuses and drains into the middle meatus. Most of the ostia open into the middle meatus and the anterior ethmoid, that together are termed the ostiomeatal complex. Adults have a high concentration of cilia in the ostia. The cilia in the sinuses beat towards the openings into the nasal cavity. The increased numbers of cilia and the narrowness of the sinus openings allow for an increased time for moisturising, and warming. Nose shape The shape of the nose varies widely due to differences in the nasal bone shapes and formation of the bridge of the nose. Some nose shapes were classified for surgeries by Eden Warwick in Nasology. These were later incorporated into a nasal index by Paul Topinard. Anthropometric studies have importantly contributed to craniofacial surgery, and the nasal index is a recognised anthropometric index used in nasal surgery. Paul Topinard developed the nasal index as a method of classifying ethnic groups. The index is based on the ratio of the breadth of the nose to its height. The nasal dimensions are also used to classify nasal morphology into five types: Hyperleptorrhine is a very long, narrow nose with a nasal index of 40 to 55. Leptorrhine describes a long, narrow nose with an index of 55–70. Mesorrhine is a medium nose with an index of 70–85. Platyrrhine is a short, broad nose with an index of 85–99·9. The fifth type is the hyperplatyrrhine having an index of more than 100. Variations in nose size between ethnicities may be attributed to