<prompt> Axillary sheath is an extension of-Pretracheal fasciaPrevertebral layer of deep cervical fasciaInvesting layer of deep cervical fasciaNone  <response>: Ans. is b i.e., Prevertebral layer of deep cervical fascia Axillary sheath and fascia around trunk of brachial plexus are derived from prevertebral fascia prevertebral layer of deep cervical fascia. 