_tricuspid_ valve. It is suspended from a thin ring of connective tissue
which surrounds the opening, and its free margins extend into the
ventricle (Fig. 16). It consists of three parts, as its name implies,
which are thrown together in closing the opening. Joined to the free edges
of this valve are many small, tendinous cords which connect at their lower
ends with muscular pillars in the walls of the ventricle. These are known
as the _chordæ tendineæ_, or heart tendons. Their purpose is to serve as
_valve stops_, to prevent the valve from being thrown, by the force of the
blood stream, back into the auricle.

The _mitral_, or bicuspid, valve is suspended around the opening between
the left auricle and the left ventricle, with the free margins extending
into the ventricle. It is exactly similar in structure and arrangement to
the tricuspid valve, except that it is stronger and is composed of two
parts instead of three.

[Fig. 16]


Fig. 16—*Right side of heart* dissected to show cavities and valves. _B._
Right semilunar valve. The tricuspid valve and the chordæ tendineæ shown
in the ventricle.


The _right semilunar_ valve is situated around the opening of the right
ventricle into the pulmonary artery. It consists of three pocket-shaped
strips of connective tissue which hang loosely from the walls when there
is no pressure from above; but upon receiving pressure, the pockets fill
and project into the opening, closing it completely (Fig. 16). The _left
semilunar_ valve is around the opening of the left ventricle into the