(Chapter 14) Footnote 14:

Paraphrased from Galen De usu partium 4.42.2: “Nature has made the spine for animals to be like the keel of body that is necessary for their life; for it is thanks to the spine that we can walk erect and each of the other animals can walk in the posture that is better for it .... She has, however, wished the spine to be useful not only for this. Just as her custom is always to work artistically and employ one construction of a part for many uses at once, so it is in this instance too; ...” tr. May 1968, p. 570. On Galen’s frequent comparison of the spine to a keel, see May p. 159 n. 10.