7 66 



HANDBOOK OF PHYSIOLOGY — CIRCULATION II 



V. pulmoiLilb dcxtra 



\trium Binblrum 



V i iv tpei 



Aiin< nl i sinistra 



fig. 6. Superficial muscle layers of the 

 maximally contracted human heart, seen 

 from the ventrocranial aspect after separation 

 of the atria (above) from the ventricles (be- 

 low). The position changes of the great vessels 

 and the ventricle outlines during relaxation 

 are indicated by dashed lines. [From Spalte- 

 holz (148).] 



A. pulmonalis 



i^iiuam.ilis 

 anterior 



Ventriculus dexter 



iDcfsura [apicfe ■ ordfc 



Apex coidis 



Vol ti & tunlii 



According to Benninghoff (10), who uses a somewhat 

 different classification, there are three interconnected 

 systems which intersect rectangularly: a) the outer 

 longitudinal fibers which connect to the outer contour 

 fibers at the ostia; b) the ring fibers which encircle the 

 entire chamber and curve around to form fibers of 

 the ventricular septum; c) the internal longitudinal 

 fibers which run from the contour fibers toward the 

 apex (figs. 11 and 12). Benninghoff (10) analyzed 

 the function of these various bundles on the basis of 

 careful comparative anatomical studies and in vivo 

 observations. He emphasized the concept that 

 crossing of the fiber layers at right angles results in an 

 over-all reduction of the cavity size, as first postulated 

 by Carl Ludwig. Each of the three systems affects the 

 entire heart and at the same time each of the ventric- 



ular cavities. They act in such a manner that a 

 reduction of the heart chambers does not occur 

 equally in all directions but in such a manner and 

 sequence that the cavities are emptied toward their 

 outflow tracts. The evolution proceeded as follows: in 

 lower vertebrates (fish, amphibia) there are no 

 tendinous elements and all muscle bundles are ring 

 shaped. In the mammalian heart secondary valves 

 (atrioventricular) are formed from which the con- 

 nective tissues of the fibrous rings of the atrioventricu- 

 lar valves and of the chordae tendineae originate and 

 become inserted into the course of the ring-shaped 

 muscle. The fibrous rings become connected to the 

 roots of the arteries and form the solid trigona fibrosa, 

 which furnish new insertions for many myocardial 

 fibers (see fig. 4). In the evolutionary process the 



