Methodology and Material
The five orangutans examined in this study were made available by the following institutions: George Washington University (P. pygmaeus, GWU PP1, adult male, formalin embalmed), Howard University (P. pygmaeus, HU PP1, neonate male, formalin embalmed), and Valladolid University (P. pygmaeus, VU PP1, adult female, fresh, provided by the Zoo-Aquarium of Madrid; P. pygmaeus, VU PP2, adult female, fresh, provided by the Bioparc Fuengirola of Malaga; P. abelii, VU PA1, adult female, skeleton, provided by the Zoo de Santillana of Cantabria). We took photographs of the musculoskeletal system of all of the specimens we dissected; the muscle weights listed in this atlas are from the VU PP1 and VU PP2 specimens (total body weight = 72 and 61 kilograms, respectively), which were in particularly good condition. The photographs of the osteological structures shown in this atlas are from the VU PA1 and VU PP2 specimens. In the text below, when the data are available, we provide for each muscle: 1) its weight in the VU PP1 and VU PP2 specimens. The total mass of all the striated muscles is given in parentheses immediately following the name of the muscle. In the case of paired muscles, the muscles of the left and right sides are referred to as LSB and RSB, respectively. When the muscle is part of a symmetrical structure (e.g., stylohyoideus), the weight given is that of the muscle of one side of the body; when the muscle is unpaired (e.g., diaphragm), the weight given is that of the part of the muscle that comes from one side only; 2) the most common attachments and innervation of the muscle within the orangutan clade, based on our dissections and on our literature review; 3) the function of the muscle (e.g., based on electromyographic-EMG-studies); 4) comparative notes, especially when where there are differences (e.g., regarding the presence/absence of the muscle, or of its bundles, its attachments, and/or its innervation) between the configuration usually found in orangutans and the configuration found in a specimen dissected by us (in these cases we often provide photographs to illustrate the differences) or by others; and 5) a list of the synonyms that have been used by other authors to designate that muscle.