An understanding of blood flow requires a detailed picture of vascular and microvascular anatomy. To this end an investigation of the arteries feeding the spinotrapezius muscle in normotensive and spontaneously hypertensive rats was performed. Arteries were dilated and filled with resin materials and analyzed quantitatively for their network pattern and vessel geometry. The results show that there exists extensive meshworks of interconnected arteries forming an interorgan plexus. The spinotrapezius muscle has multiple inflows from the thoracodorsal and intercostal arteries which interconnect in an arcade network in the muscle. Some but not all arteries of hypertensive rats are narrower in the dilated state at 100 mm Hg inflation pressure than their controls. Arterioles within the muscle proper, however, are not significantly different, suggesting that lumen narrowing of structural origin is progressively reduced towards the microcirculation.