Suspensory activity of Japanese macaques was reported in this study. Study site is the Tsubaki Wild Monkeys Park in Wakayama Prefecture in Japan. The subjects were 15 identified individuals which were provisioned. Focal sampling method was adopted. Hanging by arm (s), by leg (s) and by arm (s) and leg (s) were all observed. Hanging often attends limb rotation, limb joint extension and palmer flexion. But both forelimb (s) and hindlimb (s) hanging doesn't so much need knee or hip joint extension. Hindlimb (s) hanging goes with the wider limb rotation in younger animals. Both the frequency and duration of all suspensory activity were significantly (but inversely) correlated with age class. Hindlimb (s) hanging and both forelimb (s) and hindlimb (s) hanging were never observed in adult age class animals. But adult individuals adopted forelimbs suspension although that frequency was low. The ontogenetic change of suspensory activity may be related to the decrease in limb joint mobility as well as in relative weight of the digital flexors to body weight. The attribute of Japanese macaques suspensory activities are different from that of other primates suspensory behavior. Hanging is an important component of various positional behaviors which constitute one arboreal transferring session. All age class individuals adopted hanging when they transferred a vertical wide gap, whereas suspensory activity has never observed in feeding and horizontal transferring in adult age class individuals. Suspensory activities observed in transferring ended in short moments in Japanese macaques. But under another situation (ex. play, horizontal transferring and so on), suspensory activities were observed in younger age class and lasted rather long period.

View full abstract

In order to clarify the condition of the change from the horizontal quadrupedal walking to the vertical climbing in a Japanese macaque, we made an experiment on the inclined substrata. The subject was an adult male Japanese macaque. It freely moved on the substrata, a bamboo pole (8cm diameter). The inclination of the substrata was changed from 15 degrees to 65 degrees with each 5 degrees and the number of the steps was eleven. We put the surface extrodes and telemetry transmitters on the subject to record the activity of the triceps brachii and the biceps brachii. The patterns of the electromyography were clearly different between the horizontal quadrupedal walking and the vertical climbing.
The palm of the Japanese macaque touched the substrata on the behind side in the vertical climbing. It was found that this type of forelimb use was observed in the inclination of 50 degrees or more. The cycle duration also decreased at the inclination of 50 degrees or more. The relative duration of stance phase of the forelimb decreased at the inclination of 65 degrees and that of the hindlimb increased at the inclination of 55 degrees or more. The electromyography study showed three stages. The first stage was similar to the horizontal quadrupedal walking and it was seen at the inclination of 15 degrees or less. The second stage was the intermediate type and it was observed between the inclination of 20 degrees and 50 degrees. The last stage was similar to the pattern of vertical climbing at the inclination of 55 degrees or more. These results of electromyography were related to the difference in the locomotor function of the forelimb at different degrees of inclination.

View full 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.

View full abstract

The static implications of the fiber architecture, i. e., the orientation of a muscle's line of action, fiber bundle length and physiological cross-sectional area of the scapulohumeral muscles, were analyzed 3-dimensionally using five Japanese macaques. The results are as follows: 1. The teres major and deltoids, whose ∠ε (the angle formed between the humeral long axis Ax and CI, where C: geometrical center of humeral head; I: muscle insertion) is close to zero, work exclusively as a humeral circumducer irrespective of humeral orientational change. In contrast, in the remaining muscles whose ∠εis large, the actual humeral spatial orientation or ∠δ (the angle formed between Ax and Poic, the plane passing three points of O, I, and C; O; muscle origin) decides the action of a muscle. It was theoretically shown that at the humeral resting position the infraspinatus and subscapularis acts as a rotator, the supraspinatus as a circumducer, and the teres minor as an intermediator. 2. The muscle excursion range, and the certain limited rotatory range of OI about OC demarcate the potential maximum range of I (RmaxI) on Soc (the sphere centered at C with its axis passing O and C). Since Ax can rotate about CI, the potential maximum range of Ax (RHP) and the rotatory range of CI about Ax (RHR) are then geometrically given on Soc. Again, the potential maximum moment about C (MaxPot. |Nt|) is given as a function of I's site in RmaxI. In the muscles with a small ∠ε, RHP approximately overlaps RmaxI. Thus they are considered to have a higher maneuverability of Ax, with a value of MaxPot. |Nt| as an approximate function of the Ax' site. The knowledge obtained in the present study provides a theoretical basis for clearly defining how the shoulder musculoskeletal system of primates evolved through their arboreal lives.

View full abstract

Skeletal muscles of primates are composed of fast-twitch/glycolytic (FG), fast-twitch/oxdative/glycolytic (FOG), and slow-twitch/oxidative (SO) myofibers, which are classified by differences in histochemical reactivity of reduced nicotinamide adenine dinucleotide dehydorgenase, mitochondrial glycerol-3-phosphate dehydrogenase, and myosin ATPase. The postural muscles have many SO myofibers. The locomotory muscles have many fast-twitch (FG and FOG) myofibers. The limb muscles of Japanese macaques, rhesus macaques, lesser bushbabies, and gray lesser mouse lemurs contain FG, FOG, and SO myofibers, whereas the muscles of slow lorises have FOG and SO myofibers and no FG myofibers. SO myofibers are involved in postural maintenances and function in preventation of fall from trees. FOG myofibers are used for continuous movements and locomotary and FG myofibers for short bursts of high activity. The SO and FOG myofibers are necessary for climbing a tree and living on a tree, adaptation to aloreality. Although the FG myofibers are dispensable in arboreal monkeys, they are developed greatly in primates' muscles that generate a large propulsive force for running, climbing, jumping, and leaping. The composition of myofiber types differs in analogous muscles. The differences are correlated with locomotory patterns of primates.

View full abstract

The morphology of the femur varies among the anthropoid primates reflecting different positional behaviors. Femora of cercopithecids are adaptive for cursorial locomotor patterns (e. g., running, leaping) but less adaptive for climbing or clambering. Femora of colobines are more specialized for leaping and arboreal balance as compared with those of cercopithecines. Femora of medium- and large-sized cebids, chimpanzee, and gibbon display morphological features related to quadrumanous climbing and acrobatic arboreal balance, but they demonstrate no specialized feature for cursorial locomotion and leaping. Outstanding characteristics in each taxon are as follows: projected greater trochanter and anteroposteriorly long distal epiphysis in cercopithecines; thick and more or less acutely angled neck, and symmetrically sized femoral condyles in colobines; low greater trochanter, gracile and highly angled neck, mediolaterally wide distal epiphysis, and expanded medial condyle in apes; gracile and highly angled neck, and mediolaterally wide distal epiphysis in medium- and large-sized cebids.

View full abstract

The direction of the orbits in mammals, especially in primates, was examined to explain orbital convergence in primates. The orbital axes of old world monkeys are between 40°∼50°, while those of new world monkeys exceed 50°. The orbital axes tend. to be even larger in callithricids. In Prosimians, the axis angle ranges from 60°∼100°, and is clearly larger than those of the anthropoids. The orbital axis angle of carnivores is between those of prosimians and anthropoids. However, their orbital planes have not turned to the front, because the olfactory sense is also important for them. Ungulates have large orbital axis angles over 100°. It is clear that arboreality is possible even if the orbit has not turned to the front as it is in anthropoids, because tree shrews or squirrels do not have orbits rotated to the front as in anthropoids. Carnivores, although they are terrestrial mammals, have orbital axis angle as small as in primates. As a result, the frontal rotation of the orbit was not caused simply by the adaptation to arboreal life, supporting the visual predation hypothesis advocated by Cartmill (1972).

View full abstract

The closure of the airway by the larynx has three functional meanings: the first is the prevention of error in deglutition, the second, trapping of the exhaled air flow inside the thoracic cavity; and the third and last, the phonation. These three functions were all present in the mammals in the early Tertiary period, ca.65 million years ago. The second function, air trapping, enables the fixation of the thoracic cage, which is essential for obtaining the supporting points for the shoulder girdle musculatures during movements of the upper extremities. This anatomical innovation is originated in the three-dimensional, discontinuous arboreal habitat of the early mammals, and further elaborated in the tree-dwelling primates as the safety device to prevent falling from the tree. The specificity of the primate larynx is the completely closed anterior glottis during the air trapping. Although the complete closure of the anterior glottis is emphasize in the modern human as the adaptation to the production of primary tones, its functional origin goes back to the three-dimensional locomotor adaptation in the Tertiary arboreal primates.

View full abstract

Occurrence of the laryngeal constriction, i. e. air trapping, which is thought to stabilize the thorax to assist the upper limb movements, were investigated in behaving human subjects by means of endoscopic and EMG recordings. Subjects employed in the experiments were 4 Japanese sports men; a Judo player, a Kendo player and two gymnasts. In two gymnasts; one won a silver medal at the 1984 Los Angeles Olympic, and the other one held the All Japan Gymnastics Championship (horizontal bar) title for five consecutive years. They were asked to perform brachiation. Laryngeal dynamic gestures were recorded by means of a specially designed endoscopic video system. EMGs were recorded for 8 muscles of the upper extremity and shoulder girdle using surface electrodes. Side view motion pictures of the behaving subjects were recorded by a video camera. Signals of the video frame (laryngeal gestures and motion pictures) were simultaneously recorded with the EMGs. During brachiation, the strong laryngeal sphincteric actions were consistently recognized in the case of Judo and Kendo players. However, in the case of two gymnasts, very little laryngeal closure was hardly observed throughout brachiation. In the case of Judo and Kendo players, the discharges of anterior portion of the deltoid and sternal and costal portion of the pectoralis major appeared and remarkably increased during swing phase with right arm. The laryngeal sphincteric actions were recognized at the period of increasing phase of these discharges which act for the adduction of the humerus. While, in the case of two gymnasts, the discharges of these muscles were hardly observed during swing phase with right arm. From these results, it has been strongly suggested that the laryngeal sphincteric actions are required to assist the adduction of the humerus in compensating for the increased load imposed on the shoulder joint.

View full abstract