Final answer:
The trapezius muscle elevates the scapula and assists in the lateral flexion of the neck. It is innervated by the accessory nerve and plays a role in head and shoulder movements.
Step-by-step explanation:
The muscle that elevates the scapula and laterally flexes the neck is the trapezius muscle. The trapezius is innervated by the accessory nerve, also known as the spinal accessory nerve, and it works together with the cervical spinal nerves. This muscle of the scapula enables a range of movements including extending and hyperextending the neck, rotation of the head to the opposite side when the sternocleidomastoids contract, and elevation of the scapula and clavicle, which can be demonstrated when a person shrugs their shoulders.]