Now, with all animals that are supplied with blood and furnished
with feet, and are at the same time viviparous, the bones do not
differ greatly one from another, but only in the way of relative
hardness, softness, or magnitude. A further difference, by the way, is
that in one and the same animal certain bones are supplied with
marrow, while others are destitute of it. Some animals might on casual
observation appear to have no marrow whatsoever in their bones: as
is the case with the lion, owing to his having marrow only in small
amount, poor and thin, and in very few bones; for marrow is found in
his thigh and armbones. The bones of the lion are exceptionally
hard; so hard, in fact, that if they are rubbed hard against one
another they emit sparks like flint-stones. The dolphin has bones, and
not fish-spine.