The Collaborative International Dictionary of English v.0.48:

Sarcolemma \Sar`co*lem"ma\, n. [NL., from Gr. sa`rx, sa`rkos,
   flesh + ? rind, skin.] (Anat.)
   The very thin transparent and apparently homogeneous sheath
   which incloses a striated muscular fiber; the myolemma.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sarcolemma
    n 1: an extensible membrane enclosing the contractile substance
         of a muscle fiber