Use the heart from the specimen dissected for the muscles, or from the
specimen on which the viscera were studied.
1. Study the outside (p. 275, and Figs. 115 and 116), and learn to
recognize all parts. Find the pulmonary veins (p. 275, and Fig. 116,
_g_, _h_, _i_) and cut them, thus separating the heart from the lungs.
2. The Pericardium (p. 279). In a specimen the thoracic contents of
which have not been injured, dissect the mediastinal septum from the
pericardial sac and remove fat about the great blood-vessels so as to
expose them all fully. Study their relations. Prick and inflate the
pericardium. Slit it lengthwise over the ventricles and reflect it so as
to expose its contents. Study the attachment of serous and fibrous
layers to the heart and their relation to one another.
3. In dissecting the heart follow the course of the blood, studying
each cavity with the aid of the descriptions (pp. 275-279) as you
proceed. Dissect as follows:
_a._ Remove the dorsal wall of the right auricle (p. 275) and of its
appendage except that part of it to which the venæ cavæ are attached.
_b._ Introduce the probe from the right auricle into the right
ventricle, and feel with the probe the line along which the ventricular
wall joins the septum. Cut along this line so as to turn back the
ventricular wall as a flap, which remains attached at the base of the
ventricle.
_c._ Introduce a probe through the conus arteriosus into the pulmonary
artery and cut along the probe.
_d._ Remove the dorsal wall of the left auricle and its appendage, _but
do not_ remove that part to which the pulmonary veins are attached.
_e._ Make a longitudinal incision beginning at the apex and divaricate
the lips of the cut as you pass toward the base, thus avoiding injury to
the lateral flap of the bicuspid valve. Without injury to the flap or
the columnæ carneæ, remove the heart-wall at the sides of this incision
near the base of the ventricle, as much as necessary to expose the
cavity.
_f._ Pass a probe into the aorta. Introduce scissors behind the septal
flap of the bicuspid valve and slit the aorta without injury to the
bicuspid valve.