The great Overdog
That heavenly beast
With a star in one eye
Gives a leap in the east.
He dances upright
All the way to the west
And never once drops
On his forefeet to rest.
I'm a poor underdog,
This literally refers to the travel of the constellation from East to West throughout the night as it rises and sets. Figuratively, it refers to the passage of time from birth to death. 

Canis Major