Removal of the masseter muscle reveals a system of veins and venous sinuses that are easiest to identify in the horse. The masseter muscle is composed of several bundles which are layered over the mandible. Lightly score the muscle ventral to the facial crest, sever the facial nerve near the caudal border of the mandible and the rostral border of the masseter muscle. Make a 3 to 5 mm deep cut across the masseter muscle roughly following the line of the facial nerve. Pull away a layer of muscle and cut it off near the facial crest and near the ventral border. Progressing in this fashion the vein and venous sinus will appear (transverse facial, facial, and buccal venous sinuses). These are extremely thin-walled. Take extreme care not to damage them.
Also the buccal artery vein and nerve will appear. When removing the masseter muscle appreciate the areas of origin and insertion for this muscle and its overall size.