The Pelvis of a Heron
"Pelvis of a heron (ardea herodias), nat. size, viewed from below; from nature by Dr. R.W. Shufeldt, U.S.A. dl, dorso-lumbar vertebrae to and including the last one, sc; below sc, for the extent of the large black spaces (opposite the arrow) are the true sacral vertebrae; us, urosacral vertebrae (opposite the five oval black spaces; Il, ilium; Is, ischium; P, pubis; ob, obturator foramen. The arrow flies into the acetabulum.
Elliot Coues Key to North American Birds (Boston, MA: Estes and Lauriat, 1884)
Courtesy the private collection of Roy Winkelman