Abstract: The present invention is an endoscopic over-tube for receiving and guiding medical instrumentation into the upper alimentary canal of a patient. The endoscopic over-tube has a bite block for insertion and retention in the mouth of the patient. The endoscopic over-tube also has a flexible protective sheath engaging the bite block and adapted for insertion into the upper alimentary canal of the patient. The sheath includes a stiffened region that insulates the posterior wall of the patient's pharynx from medical instrumentation as the medical instrumentation is intubated through the sheath and into the patient's alimentary canal.