Three-dimensional analysis of the arrangement and length distribution of fascicles in the triceps muscle of Galea musteloides (Rodentia, Cavimorpha)

Non-uniformity of fascicle parameters (fascicle lengths and orientation) wi thin one skeletal muscle is well known. These parameters have an effect on the physiological cross-sectional area and lengthening rate of the skeletal muscle. Using a binocular microscope with a table driver (q- and p-axes) a nd vertical drive (Y-axis) as a tool for reconstruction of the spatial orie ntation of single muscle fascicles, we developed an approach for three-dime nsional analysis of the arrangement and length distribution in the skeletal muscle of small mammals. Two subunits of the triceps brachii muscle of the Galea musteloides forelimb, triceps longum and triceps laterale, were quan tified and compared. Our data show that in the triceps laterale the fascicl es are significantly longer (10.23 mm, SD=1.19, n=41) than those in the tri ceps longum (6.58 mm, SD=2.88, n=39). In the triceps laterale, the fascicle orientation is more or less uniform, whereas, in the triceps longum, there are two areas with different orientation of fascicles: anterior and poster ior ones. Different inner architecture of the subunits can be interpreted a s an adaptation to the main locomotory function of the triceps muscle, name ly production of propulsive force during limb transfer phase and keeping dy namic stability during stance phase. Comparison of our data on the fascicle length and geometry with our previous histochemical results on G. musteloi des, shows that the anterior region of the triceps longum, which differs in the fascicle orientation, also contains a significantly larger percent of slow muscle fibres. It is hypothesised here that this small region is invol ved in keeping posture.