Abstract
In order to analyze functional morphological features of the lateral hamstring muscle of the Japanese macaques, right lower limbs of 13 individuals of theJapanese macaque were dissected and quantitative measurements were performed on the level of muscle insertion. Though the tendinous origin of this muscle is limited to a narrow area at the ischial tuberosity, its insertion widely ranged from proximal one third level of the femoral segment to distal half level of the crural segment across the knee joint. Based on the running of muscle bundles, this muscle can be divided into at least three parts; femoral attaching part, capsular attaching part and crural attaching part. These morphological grouping of the muscle bundles would be correlated with the functional differentiation because of the difference in relative location of each group to the hip and knee joints. To elucidate the functional significance of the grouping by means of morphological method, static leverage ratio in each part was estimated by the method proposed by SMITH andSAVAGE (1956). When the length of each segment, level of attachment and joint angles were given, the lengths of the lever arm and power arm could be estimated.According to the variation of the abovedescribed parameters, the analysis was made on the changes in static mechanical advantages of each part of the muscle.Because the expansion of femoral attachment gives only a slight change of the mechanical advantage, it might relate to an increase of the absolute muscle force by an increase in the number of muscle fibers. The distal expansion of the crural attachment, on the other hand, brings only a little change of mechanical advantage, when it is considered as a hip extensor. However, when it is treated as a knee joint flexor, the distal expansion reflect an enhancement of the mechanical advantage. Also because the crural part is composed of a thin muscle sheet giving a slight contribution to theabsolute muscle force, the distal extension of the crural part is not considered to be related to propulsive force, but to the postural adjustment of the crural segment during locomotion.
