Anatomy of the heart in the North American beaver (Castor canadensis).

The gross anatomy of the heart of the North American beaver (Castor canadensis) is described following the dissection of nine specimens of both sexes ranging in body weight from 10 to 26 kg. The general characteristics of the beaver heart are similar to those of other mammals. However, variations in details of anatomy exist, especially for the right atrium. The right auricle is divided into 2 appendages, one on each side of the ascending aorta. The orifices of the 3 venae cavae are guarded by a well developed valvular system. Other variations in relative size and shape exist and for these points the heart of the beaver is more closely related to that of aquatic than to that of terrestrial mammals. The heart has the form of a widened cone being transversely broad and flat from one surface to the other. The apex of the organ is formed by both ventricles except in 2 specimens in which only the left ventricle participates in its formation. The right ventricle in the beaver being relatively long and narrow, its general proportions approximate those found in the seals.