370 



The Heart. 



Ostium arteriosum clextriiin 



Ostium Tenosum sinistrum 



Ventriculus_ 

 sinister 



Ostium 



-venosum 



dextrum 



Ventriculus dexter 



415. The musculature of the ventricles of the 



heart, dissected free from one another; drawn apart; viewed from below. 



SomcAA^liat scliematically represented. 

 (On the right the superficial muscle layer is showTi, on the left tJie middle layer is represented.) 



The heart is covered on its outer surface by the visceral layer of the pericardium, the 

 epicardium, on its inner surface by the e?ulocardium ; the main mass of the wall is formed 

 of muscle, the myocardium (see Y\g. 421). 



The musculature*) of the fore-chambers, or atria (0. T. auricles) (see Figs. 413 and 414) 

 is very thin and irregular. On the posterior and especially on the anterior surface fibers go trans- 

 versely from the wall of one atrium to that of the other; otherwise the fibers run chiefly in rings 

 around the mouths of the veins and around the points of origin of the auricles (0. T. auricular 

 appendices); in the auricles themselves the fibers are irregularly arranged. In addition, fibers 

 go over into the radial fiber layer of the valvulae tricuspidalis and bicuspidalis. In the right 

 atrium another, inner muscle layer, the mm. pectinati (see p. 376), exists. Between the mus- 

 culature of the atria and that of the ventricles of the heart there is in general no connection. 



The musculature of the ventricles (see also Figs. 413 and 414, 416419) is common 

 in its most superficial layers, but otherwise separated. The most superficial layer of muscle 

 (see Figs. 413 and 414) runs obliquely, in front fi-ora the right and above to the left and 

 downward, behind from the left and above to the right and downward ; the fibers can be 

 followed in their course, behind jtartly as far as the annulus fibrosus sinister, otherT^-ise, how- 

 ever, they cannot be distinguished, for long distances, from the other bands of muscle. 



The musculature of the riffht ventricle (see also Figs. 420 and 424) is thin and 

 presents in general two lajers. The ]>ortion containing the ostium venosum presents, especially 

 distinctly in the distended heart, an external, thin, connected layer and an internal, thicker 

 layer arranged in the form uf a network. In the external layer the fibers run, in the main, 

 obliquely, behind from the left and above to the right and downward and come partly from 

 the annulus fibrosus dexter (see p. 373), partly from the upper surface of the left ventricle, 

 partly from the annulus fibrosus sinister (seep. 373), partly from the septum ; in front they go 

 partly to the upper surface of the left \-entricle, partly into the septum ; following upon these 

 oblique fibers are fibers running more or less transversely. (Continued on p. 371.) 



*) In the description of the musculature (pp. 370 and 371) the heart is thought as 

 being plac(>d with the base upward, the facies diaphragmatica backward and the apex downward. 



