Arboreal locomotor habit and the morphology of the epaxial muscles

Abstract

The superficial epaxial muscles of a dusky lutong and a white-handed gibbon were dissected to reveal the arboreal morphology of these muscles. The results were compared with those of the terrestrial primate species which have been previousl y reported. Additional dissection was made on the epaxial muscles of a dog and a cat in order to specify the general rule for the organization of the epaxial muscles. Although the epaxial muscle morphology differed in the cat and the dog, the patterns of their origin-insertion relationship were similar to any primate species. Thus the morphology of these muscles could be discussed from the view point of the locomotor adaptation. The morphological differences between arboreal and terrestrial primates were observed in the lumbar architecture of the longissimus system. The strong additional muscle bundles that originated at the lumbar mamillary process joined to the longissimus system in the terrestrial patas monkey and hamadryas baboon. These muscle bundles were not found in the arboreal dusky lutong, spider monkey and white-handed gibbon. However, the erector spinae muscles morphology varied in these arboreal species. The erector spinae aponeurosis extended to the cranial direction in the spider monkey and the gibbon, but that of the dusky lutong attached only in the relatively caudal range. The erector spinae muscles of the dusky lutong and the spider monkey less developed in lumbar region, though that of the gibbon well developed. These results would suggested that the differential strategy for the arboreal life would exist, which reflects on the epaxial muscle morphology.