. Comparative physiology of vertebrate respiration. Vertebrates -- Respiration; Physiology, Comparative. THE HEART AND CIRCULATORY SYSTEM 117. Fig. 35. Diagram of the circulation in reptiles, birds and mammals to illustrate the different places where blood can be short-circuited between the systemic and pulmonary circulations. These 'shunts' are respectively: (1) The foramen ovale, (2) an incomplete inter- ventricular septum, (3) foramen of Panizza, (4) the right systemic of reptiles, (5) the ductus arteriosus. it possible for any excess blood in one part of the system to pass across into anot
. Comparative physiology of vertebrate respiration. Vertebrates -- Respiration; Physiology, Comparative. THE HEART AND CIRCULATORY SYSTEM 117. Fig. 35. Diagram of the circulation in reptiles, birds and mammals to illustrate the different places where blood can be short-circuited between the systemic and pulmonary circulations. These 'shunts' are respectively: (1) The foramen ovale, (2) an incomplete inter- ventricular septum, (3) foramen of Panizza, (4) the right systemic of reptiles, (5) the ductus arteriosus. it possible for any excess blood in one part of the system to pass across into another portion where the pressure is not so great. With reference to the systemic and pulmonary circulation, this would clearly have advantages in early tetrapods where the lungs are relatively undeveloped and their capillary bed quite likely to be unable to take sufficiently large volumes of blood. On this view it is supposed that only when the lung had evolved suffi- ciently did it become possible for the pulmonary circulation to take the same amount of blood as the systemic circulation. For it is a condition of a complete double circulation that both circuits should be able to carry equal volumes of blood in unit time. If these persisting portions of the system do function as 'shunts', they play an important role in the functioning of the reptilian cardio-vascular system. Unfortunately, details of their working are not available and this supposition remains un- proven. The few blood pressure recordings that have been made on reptile hearts suggest, however, that the resistance to flow through the lung is not as great as has been generally Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hughes, G. M. (George Morgan). Cambridge, Mass. , Harvard University Press
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