The structure and function of the outflow routes via Schlemm's Canal are discussed. Recent measurements of the pressure in the intertrabecular space, Schlemm's canal, and the episcleral veins in monkeys indicate that most of the resistance is located between the anterior chamber and Schlemm's canal. Platelets may play a role in Schlemm's canal by occluding artificial breaks and pores which are large enough to permit contact between platelets and the subendothelial tissue. The invaginations of the endothelial cells of the inner wall of Schlemm's canal are likely to prevent such contact if the pores in their wall towards the canal are small.