A bone is a member of the hard endostructure found in most vertebrates. The default heraldic bone is the human shin-bone (tibia), or its visual equivalent (the thigh-bone or femur, the arm-bone or ulna); such a bone is found in the arms of Newton, c.1460 [RH]. This bone is palewise by default.
“Rib bones” are a specific stylization of bones, found in the canting arms (Portuguese costa) of da Costa, mid-16th C. [Nobreza xvº]. Rib bones must always be shown in pairs, issuant from the flanks of the shield; three pairs seem to be the norm.
Leanore deVertearbors bears: Argent, a chevron and in base a femur purpure.
Wiglaf Birkibeinn bears: Vert, a bone argent.
Cassandra Hobbes bears: Sable, three pairs of rib bones issuant from the flanks and on a chief argent three skulls gules.