The myology of the forelimb of the common hippopotamus, Hippopotamus amphibius

The bones, muscles, and connective tissues of the forelimb of a specimen of Hippopotamus amphibius were dissected. The pattern of muscle divisions is reminiscent of that of the pygmy hippopotamus, Choeropsis liberiensis, and more distantly related artiodactyls, such as Sus, although the proportions of muscle origins, insertions and actions may differ among the groups for some muscles, as well as do the relative proportions of the bones of the pectoral limbs and girdles. Specifically, the relative size and robustness of the M. trapezius is reduced in H. amphibius in comparison to that of C. liberiensis, although the relatively larger M. teres major and M. latissimus dorsi assume more of the functions of posteromedial limb extension and medial rotation than in the pygmy hippo. Also, together with a relatively larger M. omotransversarius and other brachial muscles, these may assist the larger H. amphibius in making movements of a head that is relatively larger and heavier than is that of C. liberiensis or Sus. The forearm, wrist, extrinsic and intrinsic forefoot muscles show a similar pattern of retention to the full complement as seen in the pygmy hippo. In constrast to the pygmy hippo, H. amphibius also retains eight carpal bones.