Sternocostal/anterior surface
2l3rd 1/3rdlnterventricular septumAnterior interventricular groove
Aortic orifice
Left ventricleAnterior papillary muscleMitral orificePosterior papillary musclePosterior interventricular groove1/3rd 2l3rd
Diaphragmaticiinferior surface
Fig. 1 8.15: Schematic transverse section through the ventricles of the heart showing the atrioventricular orif ices, papillary muscles,
and the pulmonary and aoftic orifices
is the largest (Fig. 18.12). The posterior or inferior
muscle is small and irregular. The septal muscle is
divided into a number of little nipples. Each
papillary muscle is attached by chordae tendinae
to the contiguous sides of two cusps (Fig. 18.13).
The septomarginal trabecula or moderator band is
a muscular ridge extending from the ventricular
septum to the base of the anterior papillary muscle.
It contains the right branch of the AV bundle
(Figs 18.12 and 18.14).
The cavity of the right ventricle is crescentic in section
because of the forward bulge of the interventricular
septum (Fig. 18.15).Fibrous ring Cusp
Fig. 18.13: Structure of an atrioventricular valvePulmonary orifice
Right ventricle
Septal papillary muscleTricuspid orifiieAnterior papillary musclePosterior or inferior papillary musclePERICARDIUM AND HEARTSA node
AV bundle and
left branchAV nodeRight branch of
AV bundlePurkinje fibresModerator band
Fig. 18.14: The conducting system of the heart5 The wall of the right ventricle is thinner than that
of the left ventricle in a ratio of 1:3.lntervenlliculor Seplum
The septum is placed obliquely. Its one surface faces
forwards and to the right and the other faces backwards
and to the left. The upper part of the septum is thin
and membranous and separa-tes not only the two
ventricles but also the right atrium and left ventricle'
The lower part is thick muscular and separates the two
ventricles. Its position is indicated by the anterior and
posterior interventricular grooves (Fig. 18.15).