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 valvule semilunaris).! 
The chord tendinee 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 trabecule 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 
Right atrio-ven- 
tricular orifice 
Pulmonary orifice 
Origin of left coronary 
Aortic orifice 
artery {ortic orific 
Left atrio-ventricular 
orifice 
Fie. 550.—TuHe Bases OF THE VENTRICLES OF THE HART OF THE Horse. 
The atria have been removed and the aorta and pulmonary artery cut off short. The right ventricle is dilated and the 
left ventricle is contracted. p.v., 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. 
