The Scalenus posterior
(Scalenus posticus), the smallest and most deeply seated of the three Scaleni, arises, by two or three separate tendons, from the posterior tubercles of the transverse processes
of the lower two or three cervical vertebræ
, and is inserted by a thin tendon into the outer surface of the second rib, behind the attachment of the Serratus anterior
It is occasionally blended with the Scalenus medius.