Deep Cervical Fascia

We all have been so far believing that Investing layer (the most superficial layer of Deep Cervical fascia) encloses Trapezius posteriorly , then become a single layer in the ROOF of POSTERIOR TRIANGLE and then encloses Sternocleidomastoid, again become single layer and attached in the midline to mandible, hyoid bone and down to manubrium of sternum.

 Ming Zhang, University of Otago conducted a sectional anatomic investigation with the use of E12 sheet plastination in six human adult cadavers in 2002.

The finding was amazing!!!

Investing layer was absent between sternocleidomastoid and trapezius muscles. The intervening space was fully occupied by fatty tissue that was indistinguishable from the subcutaneous tissue.
The investing layer of the deep cervical fascia is incomplete so that the carotid sheath is directly exposed to the subcutaneous tissue via a gap between the sternocleidomastoid and trapezius muscle. 

Gray's Anatomy states that the portion of the investing layer lying between the sternocleidomastoid and trapezius is made up of the areolar connective tissue rather than the dense connective tissue

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