698 



HUMAN ANATOMY. 



as the 7niisculi papillares. Quite frequently in the right ventricle and more rarely in 

 the left, a muscular band occurs, which passes across the cavity from one wall to the 

 other near the apex ; such a structure constitutes what has been termed a inoderator 

 bayid. Here and there between the columnae carneae of both ventricles minute orifices 

 of the Thebesian vessels occur. 



Around the orifices situated at the bases of the ventricles the muscular sub- 

 stance of the heart's walls passes over into dense fibrous tissue, of which the portion 



Fig. 661. 



Pulmonary aorta (pulmonary artery) 



Leaflets of 



pulmonary semilunar valve 



Corpus Arantii on posterior leaflet 



Anterior leaflet of 

 aortic valve, cut 



Septal chordae of 

 tricuspid valve 



Interventricular 



septum 



Muscle 

 of left ventricle 



Moderator band 



Anterior 

 papillary muscle 



Superior vena cava 



Systemic aorta 



Right coronary 

 artery 



Right auricular 

 . appendage 



Pectinate muscles 



Anterior leaflet of 

 tricuspid valve 



Margin of tricuspid 

 valve 



Chordae lendineae 



Coluinna carnea 



Anterior wall of heart hardened in situ and sectioned parallel to posterior surface, 

 viewed from behind ; only very small part of left ventricle is seen ; probe passes from 

 pulmonary aorta (artery) into right ventricle. 



surrounding the auriculo-ventricular orifices serves to connect the auricles and ven- 

 tricles. If the auricles and the proximal portions of the aortcE be removed, the 

 fibrous tissue will be seen to form four rings (annuli llbrosi), one corresponding to 

 each of the basal orifices of the ventricles; and, furthermore, three of the rings — 

 those surrounding the two auriculo-ventricular orifices and that of the systemic aorta 

 — will be seen to be directly in contact, while the fourth-'— that surrounding the pul- 

 monary aortic orifice — is separate from the others, although connected with the right 

 auriculo-ventricular ring by a narrow fibrous band which descends in the posterior 



