Sentence:  Reindeer are well suited to the taiga's frigid winters. They can maintain a thermogradient between body core and the environment of up to 100 degrees, in part because of insulation provided by their fur, and in part because of counter-current vascular heat exchange systems in their legs and <WSD>nasal</WSD> passages. 
Meaning of the word marked with <WSD> tags:  Of or pertaining to the nose or to the nasion