. Comparative physiology of vertebrate respiration. Vertebrates -- Respiration; Physiology, Comparative. 54 VERTEBRATE RESPIRATION Coracoid External intercostal Backbone. Vertebral rib Sternal rib Sternum Fig. 17. Diagram to show the ventilation movements of the ribs and sternum of a bird. Their position during expiration are shown by full lines. Following activity of the external intercostal muscles the positions shown by dotted lines are taken up during inspiration. direct the flow along the various respiratory tubes as had been suggested by several authors. Nevertheless, the parabronchial w
. Comparative physiology of vertebrate respiration. Vertebrates -- Respiration; Physiology, Comparative. 54 VERTEBRATE RESPIRATION Coracoid External intercostal Backbone. Vertebral rib Sternal rib Sternum Fig. 17. Diagram to show the ventilation movements of the ribs and sternum of a bird. Their position during expiration are shown by full lines. Following activity of the external intercostal muscles the positions shown by dotted lines are taken up during inspiration. direct the flow along the various respiratory tubes as had been suggested by several authors. Nevertheless, the parabronchial walls contain muscles which by contracting can vary the cross sectional area of the tube and hence vary their resistance. It is almost certain that air passes along the parabronchi during both the inspiratory and expiratory movements. There will therefore be a continuous flow of air past the areas from which the air capillaries take their origin. The absence of dead spaces near the sites of gaseous exchange is mainly the result of the bellows- like action of the air sacs. The two most probable theories of ventilation diff'er in their views concerning the direction of air flow during the two phases. 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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