Final answer:
Arrow A points to the ligamentum nuchae, a continuation of the supraspinous ligament that connects to the cervical spinous processes and extends to the skull.
Step-by-step explanation:
The ligamentum nuchae, also known as the nuchal ligament, is a key anatomical structure in the cervical spine. It extends from the external occipital protuberance at the base of the skull and attaches to the spinous processes of the cervical vertebrae. It serves to uphold the head and is a continuation of the supraspinous ligament which interconnects the spinous processes of the thoracic and lumbar vertebrae.
Given the information that the anterior longitudinal ligament is located more anteriorly on the vertebral bodies, and the ligamentum flavum connects the laminae, neither of these would correspond to the ligamentum nuchae. The posterior longitudinal ligament similarly runs internally along the posterior vertebral bodies and is not the nuchal ligament. Therefore, based on the provided chapter reference that outlines key ligament structures.