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Jacobson's organ[′jā·kəb·sənz ¦ȯr·gən]
(also vomeronasal organ), a separate division of the organ of olfaction in the majority of terrestrial vertebrates. It is named after L. Jacobson, the Danish anatomist and physiologist who discovered it in 1811.
In the embryonic period Jacobson’s organ is present in all terrestrial vertebrates, including humans, in whom it is reduced by the ninth month of intrauterine life. In amphibians the organ is an outgrowth of the olfactory sac. It is absent in some adult reptiles, including turtles, crocodiles, and chameleons. In lizards and snakes the organ is completely isolated from the olfactory cavity and communicates with the oral cavity. Birds do not have Jacobson’s organ. The organ is well developed in most mammals, although it is absent in adult cetaceans and in some chiropterans and primates.
The paired Jacobson’s organ of mammals is located at the base of the nasal septum and in the form of long tubules, the posterior ends of which are blind. Anteriorly, the ducts of the organ in some species (marsupials and rodents) open directly into the nasal cavity, but most often they lead into the parotid ducts, which open into the oral cavity from the palate and into the nasal cavity near the nasal aperture. The organ varies in size, for example, from 8–9 cm long in a bull to 17 cm long in a buffalo. It is lined with sensory epithelium containing specialized receptor cells whose processes form a special branch of the olfactory nerve—the vomeronasal nerve.
The function of Jacobson’s organ has not been fully studied. It is used by snakes and lizards during their search for prey and for a mate. The molecules of odorous substances are transmitted to the receptors of the organ by means of the tongue, with which the animals probe surrounding objects. In mammals the organ participates in the perception of odors that guide sexual behavior.
REFERENCEBronshtein, A. A. Oboniatel’nye retseptory pozvonochnykh. Leningrad, 1977.
A. V. MINOR