Forearm muscles in the black lion tamarin (Leontopithecus chrysopygus)

Leontopithecus chrysopygus (black lion tamarin) is a platyrrhine primate found in the Brazilian Atlantic Forest. This species is threatened by human activities that encroach on its habitat. Studies on Leontopithecus myology provide insights into ecological variables and support primate medicine. This study aimed to analyze the anatomy of the forearm muscles of L. chrysopygus. For this purpose, six thoracic limbs from five adult male L. chrysopygus specimens were dissected. The muscles were described by their attachment points (origin and insertion), and their masses were measured using a precision scale. Functional muscle groups were established for comparison purposes. The positioning and skeletal attachments of the muscles resembled existing descriptions for primates. However, intraspecific variations were noted, such as a recess for the radial nerve between the origin of the tendon of the brachioradial muscle in one-third of the samples. The deep digital flexor muscle had the highest mean mass (2.34 ± 0.43 g), whereas the extensor muscle of the second digit had the lowest mean mass (0.03 ± 0.01 g). The carpal and digital flexor muscles showed a significantly higher mean percentage mass (p < 0.05) than the others (58.4 ± 2.7%), possibly due to the strength required for hand grip during locomotion on branches and climbing trees. Further studies on the muscles of other regions of the thoracic limb and other Leontopithecus species could enhance our understanding of how these muscles adapt to their lifestyles.