The Collaborative International Dictionary of English v.0.48:

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.
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         And Jacob said . . . with my staff I passed over this
         Jordan, and now I am become two bands.   --Gen. xxxii.
                                                  9, 10.
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         Thy name shall be called no more Jacob, but Israel.
                                                  --Gen. xxxii.
                                                  28.
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   Jacob's ladder.
   (a) (Bot.) A perennial herb of the genus Polemonium
       (Polemonium 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.
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The Collaborative International Dictionary of English v.0.48:

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