Source : Webster's Revised Unabridged Dictionary (1913)

Subcutaneous \Sub`cu*ta"ne*ous\, a.
   Situated under the skin; hypodermic. --
   {Sub`cu*ta"ne*ous*ly}, adv.

   {Subcutaneous operation} (Surg.), an operation performed
      without opening that part of the skin opposite to, or
      over, the internal section.

Source : WordNet®

subcutaneously
     adv : below the skin; "inject subcutaneously"