The inland bearded dragon (Pogona vitticeps\textit{Pogona vitticeps}Pogona vitticeps) is a terrestrial reptile native to Australia. Like all reptiles (excluding crocodilians), it possesses a double circulatory system, but its ventricle is only partially divided by an incomplete muscular septum.
Define the term double circulatory system\textit{double circulatory system}double circulatory system.
Explain how this incomplete septum makes the transport of oxygen to body tissues less efficient than in a mammal with a fully partitioned four-chambered heart.
During extreme heat, the bearded dragon retreats into deep underground burrows. Explain why the bearded dragon may die if the concentration of oxygen in the burrow's air becomes extremely low.