Variations in the Gross Anatomy of the Heart of Rana pipiens

There were three purposes for this study. The first purpose was to determine the normal anatomy of the major structure of the heart of Rana pipiens. The second purpose was to determine if any variations or anomalies existed in these structures. The third purpose was to determine if any similarity existed between any variations found and the hearts of other animals.

The normal anatomy of the frog heart, as described in most books, is either incomplete, wrong, or applies to species other than Rana pipiens. In no case was there an adequate description found of the heart as possessed by Rana pipiens. For this reason, a study of the anatomy of the heart of Rana pipiens is important.

In the evolution of the frog, there are so many factors involved that none of the frogs has a definite or set anatomy. On the contrary, some measure of variation occurs in every animal. This study dealt only with the gross variations in the major structures of the heart and did not include a microscopic examination or an examination of the minor structures, such as the valves.

The importance of similarities of structures of different species of animals in the study of evolution is very great. To show that a variation of a structure has a similarity to the corresponding structure in another species may indicate a genetic relationship between the two. Variations may show the trends of evolution or may show regressions to more primitive conditions. Sometimes, however, they are simply abnormalities in the development of the individual animal.