In man,

above all other animals, the terms 'upper' and 'lower'
are used in harmony with their natural positions; for in him, upper
and lower have the same meaning as when they are applied to the
universe as a whole. In like manner the terms, 'in front', 'behind',
'right' and 'left', are used in accordance with their natural sense.
But in regard to other animals, in some cases these distinctions do
not exist, and in others they do so, but in a vague way. For instance,
the head with all animals is up and above in respect to their
bodies; but man alone, as has been said, has, in maturity, this part
uppermost in respect to the material universe.