____________ encloses thyroid, responsible for its movement during swallowing

The correct option is Pretracheal fascia.

To understand why the pretracheal fascia is responsible for enclosing the thyroid gland and facilitating its movement during swallowing, we can break down the anatomical relationships step-by-step:

1. Anatomy of the Pretracheal Fascia:
The pretracheal fascia is a thin, layer-like subdivision of the deep cervical fascia of the neck. It is limited to the anterior part of the neck, extending from the hyoid bone superiorly into the thorax inferiorly, where it blends with the fibrous pericardium covering the heart.

2. Enclosure of the Thyroid Gland:
As the pretracheal fascia descends from the hyoid bone, it splits into two layers to invest (enclose) the thyroid gland, trachea, and esophagus. By forming a sheath around the thyroid gland (often referred to as the false capsule of the thyroid), it anchors the gland securely to the surrounding structures.

3. Mechanism of Movement During Swallowing:
The pretracheal fascia is structurally attached to the hyoid bone and the thyroid cartilage of the larynx. When we swallow (deglutition), the suprahyoid muscles contract and elevate the hyoid bone and the larynx.
Because the thyroid gland is enclosed within the pretracheal fascia, which is firmly bound to these moving cartilaginous structures of the larynx, the thyroid gland is pulled upward along with the larynx and trachea. This upward movement is a characteristic clinical sign used during physical examinations to distinguish thyroid masses from other neck masses.

4. Distinguishing from Other Options:
- Prevertebral fascia encloses the vertebral column and the deep muscles of the back/neck.
- Investing layer of the deep cervical fascia is the most superficial layer of deep fascia that surrounds the entire neck like a collar, enclosing the trapezius and sternocleidomastoid muscles.
- Superficial fascia lies immediately under the skin and contains the platysma muscle, but does not wrap deep visceral organs like the thyroid.