# 79 - Heart, human fetus, l.s.

# 80 - Heart, rat, l.s., h-e

# 46 - Muscle, heart, intercalated disks

Examine # 79 by eye before you place it on the microscope stage. Locate the thick muscular wall of the left ventricle and the thinner wall of the right ventricle adjacent to it. Note the postitions of the atria. Some of your sections may contain a portion of the right atrioventricular valve. Examine the features of the endocardium, myocardium, and epicardium. Review the histology of cardiac muscle

Does the section on your slide contain Purkinje fibers? Purkinje fibers are larger and paler than normal cardiac muscle cells, and lie just under the endothelial and subendothelial connective tissue. The myofibrils in these modified cardiac muscle cells are reduced, giving these cells a paleappearance .

Use the chart, "Comparison of Atrium and Ventricle of the Heart" in the introduction to this exercise, to compare the histological characteristics of the atria and ventricles. The chambers with the thickest walls are the ventricles. Can you see the trabeculae carnae (ridges and folds of the myocardium in the ventricles)?

References: Ross, p. 320 Gartner, p. 163, Fig. 1 -3 Wheater, p. 140 - 142, Fig. 8.1, 8.2, 8.3, 8.4, 8.5 DiFiore, p.117, Fig. 8-5 p. 119, Fig. 8-6, 8-7, 8-8