 It is covered by the skin, the superficial and deep fasciæ, and by the Platysma below.The accessory nerve is directed obliquely across the space from the Sternocleidomastoideus, which it pierces, to the under surface of the Trapezius; below, the supraclavicular nerves and the transverse cervical vessels and the upper part of the brachial plexus cross the space.The roof of this triangle is formed by the cutaneous nerves of cervical plexus and the external jugular vein and platysma muscle.