Page 51 - Clinical Anatomy

ECA1 7/18/06 6:31 PM Page 36

36 The Thorax

Fig. 29◊The coiling of the
primitive heart tube into
its definitive form.

Fig. 30◊The development of the chambers of the heart. (Note the septum primum
and septum secundum which form the interatrial septum, leaving the foramen
ovale as a valve-like opening passing between them.)

endocardial cushions. Before fusion is complete, however, a hole appears in
the upper part of this septum which is termed the foramen secundum in the
septum primum.
A second membrane, the septum secundum, then develops to the right of
the primum but this is never complete; it has a free lower edge which does,