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RUDIMENTARY NOSE. “The first vertebrates were jawless fish named agnathans who are classified in the phylum Chordata and subphylum Vertebrata and whose fossil ancestors can be traced back to the Cambrian period around 500 million years ago. Living agnathans display a primitive or rudimentary olfactory organ.” http://www.wjgnet.com/esps/DownLoadFile.aspx?Type=Digital&SubType=2&DOI=10.5319%2Fwjo.v6.i2.33&FilePath=Pub%5C10.5319%5Cv6%5Ci2%5CWJO-6-33.doc View in LinkedIn

FRAGMENT FROM NATURE considers for this and next weekend how humans came to have a nose. Embryologically, it is complex, and this only starts to make sense when comparative anatomy and evolutionary considerations come into the picture, resulting in a truly excellent case study of evo-devo (evolutionary/development) perspective on this hybrid organ. Viewing life forms from an evolutionary perspective made sense of inscrutable biology. But adding development int the mix solved Gordian knots. View in LinkedIn

ACROSS TAXA. “Phylogenically, the respiratory nose develops between mouth and olfactory nose by rearrangement of the dermal bones of the secondary palate, which appears in early tetrapods. During development, the palatal shelves develop into the palatine processes of the maxillary bones, and with the vomer, palatine, pterygoid and inferior turbinate bones form the walls of the nasal cavity after regression of the transverse lamina.” http://www.wjgnet.com/esps/DownLoadFile.aspx?Type=Digital&SubType=2&DOI=10.5319%2Fwjo.v6.i2.33&FilePath=Pub%5C10.5319%5Cv6%5Ci2%5CWJO-6-33.doc View in LinkedIn

EVOLUTIONARY CLUES. “Two major questions which can be addressed to this classic description are why the nose is formed by such a complex intricacy of different anatomical structures, and why the origin and formation of these are not found in the classic embryological description. Examining the formation of the nose in the evolution of species may, actually, give clues to the answers.” http://www.wjgnet.com/esps/DownLoadFile.aspx?Type=Digital&SubType=2&DOI=10.5319%2Fwjo.v6.i2.33&FilePath=Pub%5C10.5319%5Cv6%5Ci2%5CWJO-6-33.doc View in LinkedIn

TWO SOURCES. “According to classical concept, the philtrum of upper lip, the nasal dorsum, septum, and primary palate originate from the development of the intermaxillary process, whereas the lateral walls of the nasal pyramid develop from the lateral nasal processes.” http://www.wjgnet.com/esps/DownLoadFile.aspx?Type=Digital&SubType=2&DOI=10.5319%2Fwjo.v6.i2.33&FilePath=Pub%5C10.5319%5Cv6%5Ci2%5CWJO-6-33.doc View in LinkedIn

DEVELOPMENT CLUES. “During development, infolding of the olfactory placodes occurs, bringing the medial olfactory processes to form the septolateral cartilage while the lateral olfactory processes form the alar cartilages. The olfactory fascia unites these cartilages to the olfactory mucosa, that stays separated from brain by the cartilaginous olfactory capsule (the ethmoid bone forerunner).” http://www.wjgnet.com/esps/DownLoadFile.aspx?Type=Digital&SubType=2&DOI=10.5319%2Fwjo.v6.i2.33&FilePath=Pub%5C10.5319%5Cv6%5Ci2%5CWJO-6-33.doc View in LinkedIn

SMELL FIRST. “The median nasal septum develops inferiorly from the roof of the nasal cavity. These valuable embryologic data do not explain the complex intricacy of the many anatomical structures comprising the nose. The evo-devo theory offers a rational explanation to this complex anatomy. Phylogenically, the nose develops as an olfactory organ in fish before becoming respiratory in tetrapods.” http://www.wjgnet.com/esps/DownLoadFile.aspx?Type=Digital&SubType=2&DOI=10.5319%2Fwjo.v6.i2.33&FilePath=Pub%5C10.5319%5Cv6%5Ci2%5CWJO-6-33.doc View in LinkedIn

Anastomosis of two genetically distinct individuals. View in LinkedIn

THE HUMAN NOSE. “In humans, the mammalian olfactory chambers are transformed into olfactory clefts and lateral masses of the ethmoid, and the transverse lamina separating the olfactory and respiratory noses has disappeared.” http://www.wjgnet.com/esps/DownLoadFile.aspx?Type=Digital&SubType=2&DOI=10.5319%2Fwjo.v6.i2.33&FilePath=Pub%5C10.5319%5Cv6%5Ci2%5CWJO-6-33.doc View in LinkedIn