Circulation is covered pretty well in Kardong chapter 12 so I am not putting up a full page of notes but I am adding some new data and corrections to Kardong's text.
Lizards and turtles. In Kardong, Figure 12.32 is incorrect and should not be used for study. Essentially, the primitive reptilian pattern is a ventricle with three chambers: A dorsal cavum dorsale divided into a cavum arteriosum (CA) by the interventricular septum (IVS) and a cavum venosum (CV) and a ventral chamber, the cavum pulmonale (CP), which is partially separated from the CV by a muscular ridge. There are two entrances into the ventricle: right atrial blood empties into the CV which then spills over the muscular ridge into the CP. Left atrial blood empties into the CA. There are three exits from the ventricle: The pulmonary trunk exits the CP and the right and left aortic arches exit the CV. During systole, blood in the CP and CV exit primarily the pulmonary trunk because of lower resistance (pressure) than in the systemic arches. Once the left atrioventricular valves have finally closed, the interventricular foramen opens and blood in the CA squirts through the IVS into the CV. Increased contraction has caused the muscular ridge to close most of the opening between CV and CP, so the CV blood (from the CA) tends to exit the systemic (right and left) arches. The advantage of this system is that blood flow to the body (systemic) and lungs (pulmonary) can be controlled by controlling the resistance to flow in each system. This allows right to left shunts (unoxygenated blood exiting the aortic arches) by increasing resistance to flow into (and reducing blood flow to) the lungs. This is good during dives, for example, not only because the because the lungs cannot function under water, but because the higher CO2 levels decreases the ability of the hemoglobin in the blood to bind oxygen and so the last little bits of oxygen are released into the tissues.
Crocodiles. Figure 12.37 is a good figure to understand the hemodynamics (circulation) of the crocodile heart but there are new data that suggests some of the arrows in the figure are incorrect.
(1) Kardong has the air-breathing heart shunting blood from the right aortic arch to the left right aortic arch through the foramen of Panizza (FP) during systole (bottom, left heart). Axelsson et al. (1996) showed that only during the initial part of systole does blood flow through the FP from the right aorta to the left aorta. During most of systole, blood from the left ventricle passes out of and remains in the right aortic arch (so the grey arrow in the figure through the FP should be erased). The left aortic arch in crocodiles does not contribute any carotic (head) or subclavian (forelimb) branches (these are all from the right aortic arch) but instead only contributes to the celiac trunk in the abdomen. Because little to no oxygenated blood flows out the left aortic arch during systole in air-breathing crocs, the oxygenated blood to the foregut (supplied by the celiac trunk) comes from anastomoses with the superior mesenteric artery coming off the dorsal aorta, which is, of course, the continuation of the right aortic arch. Typically, in air-breathing crocs, blood from the right ventricle enters the pulmonary trunk because of less resistance than that in the left aortic arch. Interestingly, Jones and Shelton (1993) showed that after a large meal, resting air-breathing crocs can increase pulmonary resistance and shunt blood from the right ventricle into the left aortic arch (which exits from the right ventricle anyway). The increased CO2 in the blood to the foregut (via the left aortic arch) would increase blood acidity and facilitate the secretion of acid into the stomach.
(2) Kardong has the diving heart (bottom right heart) shunting blood from the right arch into the left arch through the FP and this oxygenated blood mixing with the unoxygenated blood from the right ventricle. Axelsson et al. (1996) have shown the opposite occurs. Blood is shunted in a reverse flow from the left arch to the right arch through the FP (this is called a reverse flow because the direction is opposite to the traditional theory of flow through the FP). This solves a problem that could occur without this shunt. During diving, the croc increases pulmonary resistance so little to no blood exits the pulmonary trunk to the lungs but instead exits the right ventricle via the left aortic arch. If no blood is going to the lungs none could be returning to the left atrium and then to the left ventricle. Therefore, no blood could be exiting out the right aortic arch, which supplies the blood to the head (as well as most of the body except the celiac trunk). This would be bad. Hence the reason for the reverse flow from the left arch into the right arch, which carries high CO2 blood which causes the hemoglobin to unbind its oxygen.