STRUCTURE OF THE HEART 



627 



anterior, the others right and left posterior. They are similar to those of the pul- 

 monary valve, but are much stronger. The free edge of each contains a central 

 nodule of fibrous tissue (Nodulus valvulae semilunaris)."^ 



The chordae tendineae are fewer but larger than those of the right ventricle. 

 There are two large musculi papillares, one on each side; they are usually com- 

 pound. The moderator bands are variable. Commonly two larger ones (which are 

 often branched) extend from the musculi papillares to the septum. Smaller ones 

 may be found in various places, especially at the apex. The other trabeculse are 

 fewer and less prominent than in the right ventricle. 



The interventricular septum (Septum ventriculorum) is the musculo-membran- 

 ous partition which separates the cavities of the two ventricles. It is placed ob- 

 liquely, so that one surface, which is convex, faces forward and to the right, and 

 bulges into the right ventricle; the other surface, which faces into the left ventricle. 



Origin of right coronary artery 



Conus arteriosus 



\ 



Pulmonary orifice 



Origin of left coronary 

 artery 



Right atrio-ven- 

 triaular orifice 



Aortic orifice 



Left atrio-ventricular 

 orifice 



Fig. 550. — The Bases or the Ventricles of the Heart of the Horse. 



The atria have been removed and the aorta and pulmonary artery cut o£f short. The right ventricle is dilated and the 



left ventricle is contracted, p.i)., Pulmonary valve; a.v., aortic valve. 



is concave and looks backward and to the left. The greater part of the septum is 

 thick and muscular (Septum musculare), but the upper part is thin and membranous 

 (Septum membranaceum). The latter intervenes between the left ventricle, on 

 the one hand, and the right ventricle and atrium, on the other. 



Structure of the Heart 

 The heart-wall consists mainly of peculiar striped muscle, the myocardium, 

 which is covered externally by the visceral part of the serous pericardium or epi- 

 cardium, and is lined by the endocardium. ,, , . • 



The epicardium is in general closely attached to the muscular wall, but is 

 loosely attached over the coronary vessels and the associated subepicardial fat. 

 1 These nodules are also termed the corpora Arantii. 



