The differences between the human and canine nasal passages that make dogs more macrosmatic
(keen-scented) lie not only in the amount of nerve receptors and cilia in its tissue (or epithelium) used to pick up scents, but also in the way the two sections are separated in dogs and other keen-scented animals.
In contrast, certain "macrosmatic
" species that lack excellent color vision are among those with the greatest olfactory abilities: dogs can smell odors at concentrations a hundred million times lower than humans, and a salmon uses smell to find its way back from the ocean to spawn in the stream where it was born (Herz 21-22).
Many four-legged animals including dogs have a keen sense of smell and are macrosmatic
, which means they have a greater level of olfactory function with a complex nose design, as well as a large olfactory lobe in the brain.
Furthermore, interpretation of some behaviors is confounded because they are related to olfaction in macrosmatic
species such as rodents and carnivores, and it is not clear that these behaviors have counterparts in microsmatic species like man.