The<unk>  <unk> , or Jacobson's<unk> , is an auxiliary olfactory sense<unk>  that is found in many animals and some adult humans that was discovered by Ludvig Jacobson in 1813. 
It develops from the nasal (olfactory) placode, at the anterior edge of the neural plate (cranial nerve zero). It is a chemoreceptor<unk>  which is completely separated from the nasal cavity the majority of the time, being enclosed in a separate bony or cartilaginous capsule which opens into the base of the nasal cavity. It is a tubular crescent shape and split into two pairs, separated by the nasal septum. It is the first processing stage of the accessory olfactory system, after which chemical stimuli go to the accessory olfactory bulb, then to targets in the amygdala and hypothalamus.  The<unk>  has two separate types of neuronal receptors, V1R and V2R, which are seven-transmembrane receptors that are coupled to GTP-binding proteins.   The receptors are distinct from each other and from the large family of receptors in the main olfactory system.  Evidence shows that the<unk>  responds to nonvolatile cues which stimulate the receptor neurons.  Its presence in many animals has been widely studied and the importance of the<unk>  system to the role of reproduction and social networking in animals has been shown in many studies.  Its presence and functionality in humans is widely controversial.
Vomeronasal organ
Paranasal sinus
Outer ear
Parotid duct
Lacrimal bone
Olfactory epithelium
Cochlear nuclei
Ear canal