Final answer:
The radiolucent band below the internal oblique ridge is the Mandibular canal, which contains the nerve and vessels for the lower teeth.
Step-by-step explanation:
The broad radiolucent band seen just below the internal oblique ridge is the Mandibular canal. The Mandibular canal is an opening located on the medial side of the ramus of the mandible that leads into a tunnel running down the length of the mandibular body. The sensory nerve and blood vessels that supply the lower teeth enter through the mandibular foramen and then follow this tunnel. Dentists must inject anesthetic into the lateral wall of the oral cavity before this sensory nerve enters the mandibular foramen to numb the lower teeth prior to dental work.