Muscle architecture of the upper limb in the orangutan
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We dissected the left upper limb of a female orangutan and systematically recorded muscle mass, fascicle length, and physiological cross-sectional area (PCSA), in order to quantitatively clarify the unique muscle architecture of the upper limb of the orangutan. Comparisons of the musculature of the dissected orangutan with corresponding published chimpanzee data demonstrated that in the orangutan, the elbow flexors, notably M. brachioradialis, tend to exhibit greater PCSAs. Moreover, the digital II–V flexors in the forearm, such as M. flexor digitorum superficialis and M. flexor digitorum profundus, tend to have smaller PCSA as a result of their relatively longer fascicles. Thus, in the orangutan, the elbow flexors demonstrate a higher potential for force production, whereas the forearm muscles allow a greater range of wrist joint mobility. The differences in the force-generating capacity in the upper limb muscles of the two species might reflect functional specialization of muscle architecture in the upper limb of the orangutan for living in arboreal environments.
KeywordsPongo Upper limb Muscle architecture Locomotion
The authors thank all the staff of Higashiyama Zoo and Botanical Gardens, for kindly allowing us to dissect the specimen. The authors also thank Noko Kuze for providing us with useful information on locomotor behavior in orangutans, and Dr. Toshiyuki Hayakawa for giving us the opportunity to preliminarily dissect another orangutan. Dr. John Cant and two anonymous reviewers offered very helpful comments on a previous draft of this paper. This study was supported by The Grant for the Biodiversity Research of the twenty-first Century COE (A14), Grant-in-Aids for Scientific Research nos. 17405018, 18637001 and 19405001 from the Ministry of Education, Science and Culture, Japan and by JSPS core-to-core program HOPE. This study was partly supported by the Cooperation Research Program of Primate Research Institute, Kyoto University and by the Great Ape Information Network (GAIN).
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