A 28-year-old male presents to the emergency department following a road traffic accident with left-sided facial trauma. On examination, he has pain and swelling over the left lower jaw, and when asked to bite down, his teeth do not meet normally on the left side. An orthopantomogram (OPG) is obtained. The structure marked **B** in the diagram shows a fracture line. Which of the following best explains why the structure marked **B** is the most common site of mandibular fracture?