An endoscope specially adapted for use with a disposable sheath having an outer casing and one or more internal channels. The endoscope includes a tip portion connected to a control handle through a flexible insertion tube. The insertion tube is formed by a braided wire tube covered by a flexible waterproof coating and surrounding a resilient D-shaped tube through which optical components for the endoscope extend. A longitudinally extending groove is formed in the braided tube to receive the channel(s). The groove extends perpendicular to, and makes contact with, a generally planar portion of the D-shaped tube so that the D-shaped tube can restrict deformation of the groove as the insertion tube bends. Longitudinal channels are formed on opposite sides of the groove to house control cables extending from the control handle to the tip portion. The cables are surrounded by tubes that collectively occupy the entire channel so that the tubes prevent the channel, and hence the groove, from collapsing.