Nose

Sense of direction

The wet nose of dogs is useful for the perception of direction. The sensitive cold receptors in the skin detect the place where the nose is cooled the most and this is thedirection a particular smell that the animal just picked up comes from.[1]
[edit]Structure in air-breathing forms

The nose of a tapir.
In amphibians and lungfish, the nostrils open into small sacsthat, in turn, open into the forward roof of the mouth through the choanae. These sacs contain a small amount of olfactory epithelium, which, in the case of caecilians, also lines a number ofneighbouring tentacles. Despite the general similarity in structure to those of amphibians, the nostrils of lungfish are not used in respiration, since these animals breathe through their mouths. Amphibians alsohave a vomeronasal organ, lined by olfactory epithelium, but, unlike those of amniotes, this is generally a simple sac that, except in salamanders, has little connection with the rest of the nasalsystem.[2]
In reptiles, the nasal chamber is generally larger, with the choanae being located much further back in the roof of the mouth. In crocodilians, the chamber is exceptionally long, helping theanimal to breathe while partially submerged. The reptilian nasal chamber is divided into three parts: an anterior vestibule, the main olfactory chamber, and a posterior nasopharynx. The olfactorychamber is lined by olfactory epithelium on its upper surface and possesses a number of turbinates to increase the sensory area. The vomeronasal organ is well-developed in lizards and snakes, in which itno longer connects with the nasal cavity, opening directly into the roof of the mouth. It is smaller in turtles, in which it retains its original nasal connection, and is absent in adultcrocodilians.[2]
Birds have a similar nose to reptiles, with the nostrils being located at the upper rear part of the beak. Since they generally have a poor sense of smell, the olfactory chamber is small,...