ABSTRACT
The vomeronasal organ (VNO), otherwise known as Jacobson’s organ, is a bilateral tubular structure located at the base of the nasal cavity on each side of the nasal septum. It is present in a wide variety of vertebrates and is typically enclosed along all or most of its length in a prominent bony or cartilaginous capsule. The VNO is closed at its posterior end and opens at the anterior end into the nasal cavity, via the vomeronasal duct. However, in some species, especially carnivores and ungulates, there is also a connection with the oral cavity, via the nasopalatine duct. The VNO was first described by Ludvig Jacobson in 1813 (Trotier and Døving, 1998). Jacobson provided detailed descriptions of the rich blood supply to the VNO and its innervation from the trigeminal nerve. In addition, he noted a completely separate nerve, consisting of large fascicles that innervated the organ along its length, which he was able to follow back to the main olfactory bulbs (Fig. 1). Jacobson could only guess at the function of this new organ based on its anatomical appearance. He considered the possibility that the VNO might have a sensory role. However, it was not obvious why a separate chemosensory system would be required in addition to the well-established sensory organs of smell and taste. Furthermore, Jacobson was impressed by the extensive glandular structure of the VNO and came to the reasonable conclusion that it was most likely to be a secretory organ that was nonetheless important for chemosensory function.
