A. Boundaries of the posterior triangle of the neck. 

Inferiorly. The clavicle.

B. Cross-section and lateral view of the deep investing fascia surrounding the sternocleidomastoid and trapezius muscles.

 C. Cross-section and lateral view of the prevertebral fascia covering the prevertebral muscles.

 D. Prevertebral fascia removed from the posterior triangle of the neck.