dorsum

from WordNet (r) 3.0 (2006)

dorsum
    n 1: the posterior part of a human (or animal) body from the
         neck to the end of the spine; "his back was nicely tanned"
         [syn: {back}, {dorsum}]
    2: the back of the body of a vertebrate or any analogous surface
       (as the upper or outer surface of an organ or appendage or
       part); "the dorsum of the foot"

from The Collaborative International Dictionary of English v.0.48

Dorsum \Dor"sum\, n. [L.]
   1. The ridge of a hill.
      [1913 Webster]

   2. (Anat.) The back or dorsal region of an animal; the upper
      side of an appendage or part; as, the dorsum of the
      tongue. Dortour