A quantitative analysis of blood flow dynamics in skeletal muscle requires a detailed picture of the microvascular network. This report presents an analysis of the arteriolar network structure in the spinotrapezius muscle of the rat. The microvasculature is visualized by injection of a carbon suspension and recorded in the form of photomicrographs with a complete reconstruction of the microvasculature on transparent overlays. The spinotrapezius muscle has several major feeding arterioles which supply blood into an extensive meshwork of interconnecting or arcading arterioles spanning the entire muscle. The connections from the arcade arterioles to the capillaries are provided by transverse arterioles, which branch from the arcades at regular intervals. Each transverse arteriole forms a single asymmetric dichotomous tree and within each muscle there is a wide range in the size of transverse arterioles. A new branching schema is proposed to describe the arteriolar network. A set of network parameters is derived and typical values of these parameters in the spinotrapezius muscle of the rat are provided.