[Plate 215, Left Atrium and Ventricle]page 111
page 112Right atrium
The posterior wall of the right atrium is smooth (sinus venarum) and contains the orifices of the superior vena cava and coronary sinus.
The anterior wall is ridged with the pectinate muscles.
The smooth and rough parts of the right atrium are separated internally by a smooth ridge, the crista terminalis, which presents externally
as shallow groove, the sulcus terminalis.
The superior vena cava opens into the superior aspect of the right atrium.
The inferior vena cava opens into the inferior part, in a direct line with the superior vena cava.
An interatrial septum separates the right and left atria.
An oval depression in the interatrial septum, the fossa ovalis, represents the fetal foramen ovale and its valve.
A right atrioventricular (AV) orifice opens into the right ventricleRight ventricle
The right ventricle is situated in front and to the left of the right AV orifice.
The interior has prominent muscular ridges, the trabeculae carnea.
The tricuspid valve or right AV valve usually consists of three leaflets.
The bases of the leaflets or cusps are attached to the fibrous ring around the orifice.
The free edge of each leaflet is attached to two of the three papillary muscles by tendinous cords (chordae tendinea).
The papillary muscles are three in number: septal, anterior and posterior.
These muscles contract before the ventricle itself contracts, tightening the chordae tendinea and drawing the cusps of the valve together to
prevent backflow of blood into the right atrium.
The septomarginal trabecula, or moderator band, is a free band of muscle extending from the interventricular septum to the anterior wall of
the ventricle, and it contains Purkinje fibers from the right bundle branch (see conducting system).
The outflow tract of the ventricle is separated from the inflow tract by a smooth crest, the supraventricular crest.
The outflow tract, or conus arteriosus, is smooth walled and leads to the pulmonary trunk and the valve that guards its orifice, the pulmonary
valve.
The pulmonary valve has three cusps, which open like pockets to catch regurgitated blood during ventricular diastoleLeft Atrium