The Collaborative International Dictionary of English v.0.48:

Hemal \He"mal\, a. [Gr. a"i^ma blood.]
   Relating to the blood or blood vessels; pertaining to,
   situated in the region of, or on the side with, the heart and
   great blood vessels; -- opposed to neural.
   [1913 Webster]

   Note: As applied to vertebrates, hemal is the same as
         ventral, the heart and great blood vessels being on the
         ventral, and the central nervous system on the dorsal,
         side of the vertebral column.
         [1913 Webster]

   Hemal arch (Anat.), the ventral arch in a segment of the
      spinal skeleton, formed by vertebral processes or ribs.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hemal arch
    n 1: a structure arising ventrally from a vertebral centrum and
         enclosing the caudal blood vessels [syn: hemal arch,
         haemal arch]