THE HEART 



567 



FIG. 422. The muscular arrangement of the apex of the heart. 

 (Poirier and Charpy.) 



and end in its papillary muscles. The deep layers are three in number; they arise in the papillary 

 muscles of one ventricle and, curving in an S-shaped manner, turn in at the interventricular 

 furrow and end in the papillary muscles of the oth^r ventricle. The layer which is most super- 

 ficial in the right ventricle lies next the lumen of the left, and vice versa. Those of the first layer 

 almost encircle the right ventricle, 

 and, crossing in the septum to the 

 left, unite with the superficial fibres 

 from the right auriculoventricular 

 ring to form the posterior papillary 

 muscle. Those of the second layer 

 have a less extensive course in the 

 wall of the right ventricle, and a 

 correspondingly greater course in 

 the left, where they join with the 

 superficial fibres from the anterior 

 half of the tendon of the conus 

 arteriosus to form the papillary 

 muscles of the septum. Those of 

 the third layer pass almost entirely 

 around the left ventricle and unite 

 with the superficial fibres from the 

 lower half of the tendon of the 

 conus arteriosus to form the ante- 

 rior papillary muscle. Besides the 

 layers just described there are two 

 bands which do not end in papil- 

 lary muscles. One springs from 

 the right auriculoventricular ring 

 and crosses in the auriculoventric- 

 ular septum; it then encircles the 

 deep layers of the left ventricle and 

 ends in the left auriculoventricular 

 ring. The second band is appar- 

 ently confined to the left ventricle; 

 it is attached to the left auriculo- 

 ventricular ring, and encircles the 

 portion of the ventricles adjacent 

 to the aortic orifice. 



The auriculoventricular bundle 

 of His (fasciculus atrioventricularis 

 (Fig. 424) is the only direct muscle 

 connection known to exist between 

 the auricles and ventricles. It 

 arises near the opening of the 

 coronary sinus, where it is con- 

 nected with the annular and septal 

 fibres of the right auricle. These 

 fibres converge, form a node (node 

 of Tawara), and continue as a com- 

 pact bundle which passes forward 

 in the lower part of the pars mem- 

 branacea septi to the upper limit of 

 the muscle portion of the ventricu- 

 lar septum, and divides into right 

 and left fasciculi. These run down 

 to the right and left ventricles, one 

 on either side of the interventricu- 

 lar septum, the left limb being 

 just covered by endocardium, while 

 the right limb, for a part of its 

 course, is more deeply placed in the muscle layer. Each limb is enclosed in a layer of connective 

 tissue, which isolates it from the musculature of the interventricular septum, but in the lower 

 parts of the ventricles each fasciculus separates into numerous strands which enter the papillary 

 muscles and spread over the entire internal surface of the ventricular muscle and form histological 

 connections with the true cardiac muscle fibres. The right limb is the smaller of the two and 



FIG. 423. The arrangement of the muscle of the ventricle. 

 (Poirier and Charpy.) 



