Abstract: A cannula for passing surgical instruments through tissue. In some instances, the cannula may include a distal flange flexible between a radial configuration and a longitudinal configuration. In some instances, the cannula may also include an actuator configured to move the distal flange between the radial configuration and the longitudinal configuration. In some instances, the cannula may include a valve disposed within the lumen of the cannula, and a cap configured to secure the valve to the cannula. The valve may include a body member having a base and first and second opposing walls extending from the base. In some instances, the valve has an arcuate cutout in the lower surface configured to fit around an instrument shaft inserted therethrough. In some instance, the cannula includes a slit extending an entire length of the cannular to permit an instrument shaft to be inserted and/or removed laterally.