Terrestrial and aquatic locomotion of the river otter (Lutra canadensis), the sea otter (Enhydra lutris), and the harp seal (Pagophilus groenlandicus) are successively described and analyzed in relation with the external characteristics of these species. Terrestrial locomotion, typical of land carnivores in Lutra and Enhydra, is different and extremely awkward in Pagophilus. In the water, only Lutra has to actively maintain itself at the surface; the other two species have been observed at the surface for long periods with no movements. There is an increased tendency from Lutra to Enhydra to Pagophilus toward enlarged highly specialized feet, approximating a perfect lunate border. Tail surface area decreases in the above order. The length and density of foot hairs decrease if compared with midback and tarsal regions and also from Enhydra to Lutra to Pagophilus.

The arterial pattern of the stomach of the North American beaver is studied by dissection of height specimens. The arrangement of the arteries resembles the typical mammalian pattern, although some variations are described. For example, the celiac artery gives off two large vessels, the cardiac and fundic arteries, which supply the corresponding regions of the stomach. Also, the right gastric artery originates from the gastroduodenal vessel instead of the hepatic artery.

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The heart of the beluga whale (Delphinapterus leucas) is described from the dissection of seven specimens. As in most whales the heart is characterized by a transverse broadness and a flatness of the ventricles from one surface to the other and by an apex formed by both ventricles. Heart size parameters are used for comparison with parameters of other marine and land mammals. The heart width index (heart height/heart circumference) averages 31.3 in comparison to 28.7 for the Weddell seal and 39.0 for the felids. The right ventricle is relatively long and narrow with a mean length index (TS/heart height) of 64.7 and a mean breadth index (TP/heart height) of 38.7. These heart parameters are discussed in functional terms.

The heart of the Harp seal (Pagophilus groenlandicus) is described based on the dissection of six specimens of both sexes ranging in body weight from 23.2 to 46.4 kg. The heart is characterized, as in other seals, by a transverse broadness and a flatness of the ventricles along with an apex formed by both ventricles. Heart parameters are used for comparisons with those of other seals and land mammals. The heart width index (heart height/heart circumference) averages 33.4 compared to 28.7 for the Weddell seal and 39.0 for the felids. The right ventricle of the Harp seal heart is relatively long and very broad with a mean length index (TS/heart height) of 68.8 and a mean width index (TP/heart height) of 54.8. These functional heart parameters are discussed and physiological adaptations are suggested.