Yours, Etc.: Origins and Uses of 8 Sign-Offs
Old English hrycg "back of a man or beast," probably reinforced by Old Norse hryggr "back, ridge," from Proto-Germanic *khrugjaz (cf. Old Frisian hregg, Old Saxon hruggi, Dutch rug, Old High German hrukki, German Rücken "the back"), of uncertain origin. Also in Old English, "the top or crest of anything," especially when long and narrow. The connecting notion is of the "ridge" of the backbone. Spelling with -dg- is from late 15c. Ridge-runner "Southern Appalachian person" first recorded 1917.
A long, narrow, or crested part of the body, as on the nose.