During this lab examine the preserved-mounted, hemisected heart with parts labeled, and the preserved specimens of arteries and veins, noting the macroscopic features of each.

Heart -- Two microscopic specimens of the walls of heart ventricles are on slides 64 and 65, stained with periodic acid-Schiff reagent (PAS) and with Masson trichrome respectively.

Slide 65 has some staining artifacts and folds, but shows the blood vessels and dense CT in the myocardium well. Examine the major features of the heart on both slides. An H&E stained heart specimen is on slide 139.

• Identify the three layers of the heart wall (Fig. 11-4 through 11-6).
• The thin endocardium (Fig. 11-14) is only present on the "bulges" on one side of the section.
• The myocardium (Fig. 11-4) is the thickest layer and contains cardiac muscle, connective tissue, and small blood vessels.
• The epicardium (Fig. 11-5) is a relatively thick layer of fatty connective tissue, containing small nerves and large coronary vessels.
• Identify Purkinje fibers (Fig. 11-4) of the heart's conduction system near the endocardium and epicardium.

What is unusual about the embryonic origin of Purkinje fibers in light of how they function?

The heart valves are next.