Which muscle is adjacent to the trachea and is posterior to the thyroid and the common carotid arteries?

The longus colli muscle is indeed the correct answer as it is situated adjacent to the trachea and lies posterior to the thyroid gland and the common carotid arteries. The longus colli muscle is a deep muscle of the neck that extends from the cervical vertebrae to the anterior aspect of the cervical spine, playing a role in flexing and rotating the neck. Its anatomical position makes it closely related to the trachea, allowing it to be classified as posterior to the thyroid and carotids.

In contrast, the sternohyoid muscle is more superficial and lies anterior to the trachea and surrounding structures, while the thyrohyoid muscle is also anterior, specifically associated with the thyroid cartilage. The scalenus anterior muscle, meanwhile, is positioned laterally in relation to these structures and does not fit the criteria of being adjacent to the trachea or posterior to the thyroid and common carotid arteries. Thus, the longus colli muscle is distinctly positioned to meet the criteria of the question.