The physicality of the centaur is primary to the allusion - the haunches
of goat or horse, as Terrell mentions - the upper body having the
dexterity and social skills of a human. Those haunches are the source of
power and movement, leading to rhythm. That rhythm is lithe, not heavy,
it is the great base of the emotions and dexterous skills of the upper
body, i.e, affects all above it. The ant uses its legs in a facile way,
its rhythm determined by the legs. The upper body used for dexterity.
The "poetry" or "art" found in the ant derives from two movements: the
rhythmic patterning of the ants' endeavor as a whole, and the individual
cadence of each ant. The centaur's heel plants in the earth's loam,
another way of saying things flower forth from being able to negotiate
the soft clay. The heel must depress, ie. plant, to get the spring
forward. Loam is not the most fertile soil. Some definitions of loam
include stickiness, sandy, soft, so that heavier beasts would sink in
it, inactivated, but not issue forth a plant.
The dragon, with its weight throughout the body, has no real haunches or
physical source of power other than sheer weight; it moves slowly, if at
all; its rhythm comes through its fiery breath/its internal gases and
hot air. It destroys; does not produce. Dragons are associated with
place, where a centaur is not.
On physical premise alone, the ant is productive, the dragon not. Each
has a rhythm, but that of the ant is the rhythm of art-a rhythm of
detail built upon movement that produces and does not destroy.
I do remember in previous ant/centaur discussion someone asking if the
ant couldn't just be an ant (did I recall correctly?). Pound's
observations on the relationship of innate or adapted physicality to the
type of action that ensues are, I think, grist for the other lines, and
the ant-seen in terms of its great base-is still an ant.
Dan, I've used the external references to help gain a focus on what
Pound's central ideas might be; I think they are about the physical
requirements for (detailed) movement. These ideas recur in the poetry
and music consistently. A rich passage will serve as nutriment of
impulse for other ideas, too.
Ant M