Page 47 - Clinical Anatomy

ECA1 7/18/06 6:31 PM Page 32

32 The Thorax

Right ventricle (Fig. 25)
The right ventricle is joined to the right atrium by the way of the vertically
disposed tricuspid valve, and with the pulmonary trunk through the pul-
monary valve. A muscular ridge, the infundibuloventricular crest, between
the atrioventricular and pulmonary orifices, separates the ‘inflow’ and
‘outflow’ tracts of the ventricle. The inner aspect of the inflow tract path is
marked in the presence of a number of irregular muscular elevations (tra-
beculae carneae) from some of which the papillary muscles project into the
lumen of the ventricle and find attachment to the free borders of the cusps
of the tricuspid valve by way of the chordae tendineae. The moderator band is a
muscular bundle crossing the ventricular cavity from the interventricular
septum to the anterior wall and is of some importance since it conveys the
right branch of the atrioventricular bundle to the ventricular muscle.
The outflow tract of the ventricle or infundibulum is smooth-walled and
is directed upwards and to the right towards the pulmonary trunk. The
pulmonary orifice is guarded by the pulmonary valves, comprising three
semilunar cusps.

Left atrium

The left atrium is rather smaller than the right but has somewhat thicker
walls. On the upper part of its posterior wall it presents the openings of the
four pulmonary veins and on its septal surface there is a shallow depression
corresponding to the fossa ovalis of the right atrium. As on the right side,
the main part of the cavity is smooth-walled but the surface of the auricle is
marked by a number of ridges due to the underlying pectinate muscles.

Left ventricle (Fig. 26)
The left ventricle communicates with the left atrium by way of the mitral
valve (so-called because it vaguely resembles a bishop’s mitre), which pos-
sesses a large anterior and a smaller posterior cusp attached to papillary
muscles by chordae tendineae. With the exception of the fibrous vestibule
immediately below the aortic orifice, the wall of the left ventricle is marked
by thick trabeculae carneae.
The aortic orifice is guarded by the three semilunar cusps of the aortic
valve, immediately above which are the dilated aortic sinuses. The mouths of
the right and left coronary arteries are seen in the anterior and left posterior
sinus respectively.

The conducting system of the heart

This consists of specialized cardiac muscle found in the sinuatrial node and
in the atrioventricular node and bundle. The heart-beat is initiated in the
sinuatrial node (the ‘pacemaker of the heart’), situated in the upper part
of the crista terminalis just to the right of the opening of the superior
vena cava into the right atrium. From there the cardiac impulse spreads