The Heart. 



371 



Fibers arising from the 

 annulus fibrosus sinister and going to the right ventricle 



Superficial . 

 muscle layer 



Middle (circular), 

 muscle layer 



Superficial oblique 



-bands of muscle going 



to the right ventricle 



Deep muscle_layer_- 



Vortex cordis 



416. Course of the principal layers of muscle 

 of the left ventricle of the heart, 



viewed from below. Partly schematic. 

 (Parts of the -wall of the heart have been removed above and on the left side below.) 



Musculature of the right ventricle (continued). The irmer layer is formed of short 

 bands of fibers which arise partly at the upper margin of the septum, go toward the apex, 

 turn at varying levels toward the external wall and run upward in this again, in part to 

 end as the musculi papillares , in part to reach the annulus fibrosus as trabeculae carneae ; 

 between these columns are others which are stretched out transversely^ The conus arteriosus 

 possesses an external layer of circular muscle and an internal longitudinal layer at right angles 

 to it; the latter forms longitudinal ridges in the contracted heart. 



The musculature of the left venti-icle is much thicker than that of the right and is 

 divisible into three layers of fibers, which, however, are not sharply separable from one another. 

 The supei'ficial layer is thin; its fibers arise at the annulus fibrosus sinister (see p. 373) or 

 at the ostium arteriosum sinistrum and run (the superficial more steeply than the deeper fibers) 

 in front from the right and above downward and to the left, for the most part to the apex 

 of the heart to form the vortex cordis: there they bend around into the interior and form 

 the deep innermost layer of muscle. The thick, middle layer (see Fig. 415) consists of fiber 

 bands which form closed circles, run essentially perpendicular to the axis of the heart, on the 

 outer surface however also a little obliquely, in front from the right and above to the left 

 and downward; on the inner surlace they are an-anged in the reverse direction; in their course 

 the bands of fibers are manifoldly interwoven with one another. The deep, innermost layer is 

 the continuation of the fiber bands of the superfcial layer entering into the vortex cordis. Its 

 fibers are arranged in g(^ntle spiral turns but nearly parallel to the long axis of the ventricle 

 and end either in the papillary muscles or at the annulus fibrosus sinister and at the ostium 

 arteriosum sinistrum. As the trabeculae carneae they form, in general, numerous longitudinal 

 ridges, of varying tliickness, which are connected with one another by thinner transverse beams ; 

 only the septum below the ostium arteriosum is entirely smooth. 



