The Collaborative International Dictionary of English v.0.48:

Umbilical \Um*bil"ic*al\, a. [Cf. F. ombilical. See Umbilic,
   n.]
   1. (Anat.) Of or pertaining to an umbilicus, or umbilical
      cord; umbilic.
      [1913 Webster]

   2. Pertaining to the center; central. [R.] --DeFoe.
      [1913 Webster]

   Umbilical cord.
      (a) (Anat.) The cord which connects the fetus with the
          placenta, and contains the arteries and the vein
          through which blood circulates between the fetus and
          the placenta; the navel-string.
      (b) (Bot.) The little stem by which the seeds are attached
          to the placenta; -- called also funicular cord.

   Umbilical hernia (Med.), hernia of the bowels at the
      umbilicus.

   Umbilical point (Geom.), an umbilicus. See Umbilicus, 5.


   Umbilical region (Anat.), the middle region of the abdomen,
      bounded above by the epigastric region, below by the
      hypogastric region, and on the sides by the lumbar
      regions.

   Umbilical vesicle (Anat.), a saccular appendage of the
      developing embryo, containing the nutritive and
      unsegmented part of the ovum; the yolk sac. See Illust. in
      Appendix.
      [1913 Webster] Umbilicate

WordNet (r) 3.0 (2006):

umbilical vesicle
    n 1: membranous structure that functions as the circulatory
         system in mammalian embryos until the heart becomes
         functional [syn: yolk sac, vitelline sac, umbilical
         vesicle, vesicula umbilicus]