768 HANDBOOK OF PHYSIOLOGY ^ CIRCULATION II 



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. Vortex 



fig. 12. Course of the left ventricular muscle fibers. Left: preparation of human heart after partial 

 removal of the superficial and medial muscle layers (seen from the dorsal aspect 1. Riaht: schematic 

 presentation of the course of the muscle fibers as viewed from the dorsal aspect. [From Spalteholz 

 (148).] 



vortex formation near the apex are more pronounced 

 in the mammalian than in reptile and bird hearts 

 (see fig. 1 2, right). 



Rushmer (139) points out that the division of the 

 heart musculature into "sinospiral" or "bulbospiral" 

 bundles is rather arbitrary and complicates the 

 functional analysis. He suggests the division of the 

 ventricular musculature into two groups of myocardial 

 bundles, the spiral muscles and the deep constrictor 

 muscles (fig. 13). He states in his unsurpassed descrip- 

 tion, the "functional anatomical analysis points to 

 the direction physiological experimental work should 

 pursue to verify . . . postulations and to obtain 

 quantitative measurements." 



Architecture of the Atrial Myocardium 



The atria supply blood to the ventricles through 

 three mechanisms: /) passively, during the first part 

 of their diastole, by serving as blood collecting 

 chambers as long as the atrioventricular valves are 

 closed by the high ventricular pressure; 2) still 



passively, during the second part of their diastole, by 

 serving as channels to permit the passage of blood 

 from the systemic or pulmonary veins into the ven- 

 tricles once the atrioventricular valves are opened; 

 3) actively, during atrial systole, by contracting and 

 thereby pushing some blood into the ventricles shortly 

 before the ventricular myocardium begins to con- 

 tract. Since usually only a small fraction (10-30%) 

 of the blood for ventricular filling is actively propelled 

 by the atrial musculature and the resistance to inflow 

 into the ventricular cavity is negligible, the normal 

 atrial myocardium does not need to be thick walled. 



The arrangement of the muscle fibers in the atria 

 is much simpler than that in the ventricles. Two 

 groups of fibers can be distinguished : /) those which 

 belong to one atrium only, and 2) those which are 

 common to both atria (151). 



Group 1: The fibers which lie in the wall of each 

 atrium form muscle rings around the entrance 

 orifices, i.e., the pulmonary veins in the left atrium 

 and the coronary and caval veins in the right atrium. 

 These annular fibers may act as sphincters, possibly 



