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Instructor's Note
In the course of doing this lab, the students made an interesting
observation: the auricles of the heart are larger, proportional to the atria,
in some mammals than in others. The students investigated why this should
be so, focusing on the function of the auricles. Somewhat surprisingly, they
found little literature on what the function of the auricles might be. Many
sources state that the auricles merely persist as a remnant of the early embryonic
heart, while the atria, which are developmentally derived from vessels, take
over the function. If this is the case, however, why might auricles vary so
much among mammalian species? The rat team
made one original observation which may bear on this question: they noticed
that, "The opossum and the rabbit also have proportionally large auricles.
Like the rat, they have two precavals, a right (anterior) vena cava and a
left vena cava. The rest of the mammals in lab have small auricles and only
one precaval (anterior vena cava). Based on this sample, our hypothesis is
that mammals with two precaval veins have proportionally larger auricles."
