Source : Webster's Revised Unabridged Dictionary (1913)

Jacob \Ja"cob\, n. [Cf. F. Jacob. See 2d {Jack}.]
   A Hebrew patriarch (son of Isaac, and ancestor of the Jews),
   who in a vision saw a ladder reaching up to heaven (--Gen.
   xxviii. 12); -- also called {Israel}.

         And Jacob said . . . with my staff I passed over this
         Jordan, and now I am become two bands.   --Gen. xxxii.
                                                  9, 10.

         Thy name shall be called no more Jacob, but Israel.
                                                  --Gen. xxxii.
                                                  28.

   {Jacob's ladder}.
   (a) (Bot.) A perennial herb of the genus {Polemonium} ({P.
       c[oe]ruleum), having corymbs of drooping flowers, usually
       blue. Gray}.
   (b) (Naut.) A rope ladder, with wooden steps, for going
       aloft. --R. H. Dana, Jr.
   (c) (Naut.) A succession of short cracks in a defective spar.
       

   {Jacob's membrane}. See {Retina}.

   {Jacob's staff}.
   (a) A name given to many forms of staff or weapon, especially
       in the Middle Ages; a pilgrim's staff. [Obs.] --Spenser.
   (b) (Surveying) See under {Staff}.

Membrane \Mem"brane\, n. [F., fr. L. membrana the skin that
   covers the separate members of the body, fr. L. membrum. See
   {Member}.] (Anat.)
   A thin layer or fold of tissue, usually supported by a
   fibrous network, serving to cover or line some part or organ,
   and often secreting or absorbing certain fluids.

   Note: The term is also often applied to the thin, expanded
         parts, of various texture, both in animals and
         vegetables.

   {Adventitious membrane}, a membrane connecting parts not
      usually connected, or of a different texture from the
      ordinary connection; as, the membrane of a cicatrix.

   {Jacob's membrane}. See under {Retina}.

   {Mucous membranes} (Anat.), the membranes lining passages and
      cavities which communicate with the exterior, as well as
      ducts and receptacles of secretion, and habitually
      secreting mucus.

   {Schneiderian membrane}. (Anat.) See {Schneiderian}.

   {Serous membranes} (Anat.), the membranes, like the
      peritoneum and pleura, which line, or lie in, cavities
      having no obvious outlet, and secrete a serous fluid.