Myology of the shoulder of Pontoporia blainvillei, including a review of the literature on shoulder morphology in the cetacea.

The purpose of this paper is to describe in detail the shoulder myology of the La Plata River Dolphin, Pontoporia blainvillei, and to review the literature on cetacean shoulder myology. Three fetal and one adult animal were used for the collection of morphological information. Pontoporia is less specialized in its shoulder anatomy that most delphinid cetaceans, and shares several characteristics with some mysticetes. The omohyoid and anterior serratus anterior muscles are found in both Pontoporia and the mysticete Balaenoptera, but are absent in most delphinids. The pectoralis abdominalis and three rhomboideus divisions are found in Pontoporia and Kogia, but in only a few delphinid species described in the literature. It is suggested that these characteristics are associated with a generalized use of the forelimb in Pontoporia.