Deep injury of neck always involves
Investing layer lies deep to the platysma and surrounds the neck like a collar. The surgeon has to stitch platysma muscle separately so that skin does not adhere to deeper neck muscles otherwise the skin will get an ugly scar. Ref BDC volume 3;sixth edition pg 81
Platysma
Trapezius
Sternocleidomastoid
Longus colli
Head and neck