FUNCTIONAL ANATOMY OF CARDIAC PUMPING 767 



FIG. 7. The superficial bulbospiral muscle as seen from the 

 front of the human heart. A = Aorta; M = mitral orifice; 

 P = pulmonary artery; T = tricuspid orifice; AT — anterior 

 leaflet of tricuspid valve; MT = medial leaflet of tricuspid 

 valve. A F-shaped section is cut from those fibers encircling the 

 left ventricle subendocardially, so that the mitral valve may be 

 seen. A similar band on the right is not sketched in. [From 

 Robb & Robb (136).] 



fig. 8. The superior sinospiral muscle as seen from the 

 antreior surface of the heart. Symbols as in fig. 7. Again the sub- 

 endocardial layer has been cut through in order to show deeper 

 structures. The window in the right ventricular wall shows the 

 fibers from the trabeculated area running up to the anterior 



and medial leaflets of the tricuspid valve. In both of these super- 

 ficial muscles, blood vessels follow the muscle strands as they 

 encircle the apex. [From Robb & Robb (136).] 



fig. 9. The deep sinospiral muscle as seen from the front. 

 Note the division of the muscle at the posterior inter-ventricular 

 sulcus, with fibers passing anteriorly to form most of the basal 

 two-thirds of the septum; these septal fibers lie just distal to 

 the band of the left head of origin at the base of the aorta. 

 Symbols as in fig. 7. [From Robb & Robb (136).] 



fig. 10. The deep bulbospiral muscle, a powerful sphincter 

 encircling the left ventricular base and enclosing both the 

 aorta and the mitral orifice within its sweep. [From Robb & 

 Robb (136).] 



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fig. 11. Human ventric- 

 ular myocardium after re- 

 moval of the superficial 

 muscle layers (seen from 

 the caudal aspect). [From 

 Spalteholz (148).] 



spongiosa (spongy network of muscle fibers) is 

 gradually reduced by the increasing compacta (solid 

 tissue of muscle fibers). The phylogenetic remainders 

 of the spongiosa are the muscular trabeculae, which 

 are only moderately developed in the mammalian 



heart and are almost completely replaced by com- 

 pacta in the bird heart. In this respect the birds 

 represent the highest functional development. Accord- 

 ing to Benninghoff (10) the spiral course of the 

 muscle bundles toward the heart skeleton and the 



