Preferential distribution of left and right auricular blood into the arterial arches of the Tuatara, Sphenodon punctatus

Evidence is presented which shows that in traversing the heart of the Tuatara, systemic venous blood is selectively distributed to the pulmonary arches. This selective distribution of deoxygenated blood into the pulmonary circuit occurs despite the poorly developed primary ventricular septum and the lack of a secondary septum, and yet it appears to be as effective as that seen in reptiles having these anatomical attributes.