Source : Webster's Revised Unabridged Dictionary (1913)

Periosteum \Per`i*os"te*um\, n. [NL., fr. Gr. ? round the bones;
   ? around + ? a bone: cf. L. periosteon.] (Anat.)
   The membrane of fibrous connective tissue which closely
   invests all bones except at the articular surfaces.

Source : WordNet®

periosteum
     n : a dense fibrous membrane covering the surface of bones
         (except at their extremities) and serving as an
         attachment for tendons and muscles; contains nerves and
         blood vessels that nourish the enclosed bone
     [also: {periostea} (pl)]