1. Observe the connection of the heart to the lungs, diaphragm, and large
blood vessels. Inflate the lungs and observe the position of the heart
with reference to them.

2. Examine the sac surrounding the heart, called the _pericardium_. Pierce
its lower portion and collect the pericardial fluid. Increase the opening
thus made until it is large enough to slip the heart out through it. Then
slide back the pericardium until its connection with the large blood
vessels above the heart is found. Observe that a thin layer of it
continues down from this attachment, forming the outer covering of the
heart.

3. Trace out for a short distance and study the veins and arteries
connected with the heart. The arteries are to be distinguished by their
thick walls. The heart may now be severed from the lungs by cutting the
large blood vessels, care being taken to leave a considerable length of
each one attached to the heart.

[Fig. 24]


Fig. 24—Model for demonstrating the heart.


4. Observe the outside of the heart. The thick, lower portion contains the
cavities called _ventricles_; the thin, upper, ear-shaped portions are the
_auricles_. The thicker and denser side lies toward the left of the
animal’s body and is called the _left_ side of the heart; the other is the
_right_ side. Locate the right auricle and the right ventricle; the left