Miraculously providing simple explanations
for things that are, in reality,
EXTREMELY COMPLICATED !
Why do snakes and lizards
always POKE THEIR
TONGUES out?
The answer lies in an intriguing ‘sixth sense’. An
auxilliary olfactory organ that specifically detects
heavy, non-volatile particles and is of widespread
importance in the interception of pheromones. This
will not come as a complete surprise to many with an
interest in reptiles, but what about if we told you that
lions and giraffes use a very similar structure?
Jacobson’s organ, or the vomeronasal organ (VNO)
was discovered by Frederik Ruysch in the first half of
the 18 th century and described in the early 19 th
century by Danish anatomist Ludwig Jacobson, after
which it is named. The VNO consists of a pair of
crescent-shaped tubes filled with fluid that develop as
folds in the floor of the nasal sacs. Inside these
structures is a sensory epithelium containing
specialised receptor cells that are extremely sensitive.
The VNO is surrounded by blood vessels that act as a
pumping mechanism, conveying chemical stumuli to
the receptors inside. In many cases, the VNO opens
via ducts to the nasal cavity, however, in some
animals there are also connections to the oral cavity.
In squamates (snakes and lizards), the VNO has no
opening to the nasal cavity at all, and terminates in
two small pits in the roof of the mouth. Neurones
from the VNO connect to the hypothalamus, which is
instrumental in regulating reproductive, defensive
and feeding behaviours.
Although present in the embryonic stages of all
tetrapods, the VNO is lacking or poorly developed in
adult crocodiles, turtles, birds and most advanced