from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Walking with the long axis of the body parallel to the ground. Used of quadrupeds.
from The Century Dictionary and Cyclopedia
- Carrying the body in a horizontal position, as do the majority of quadrupeds: opposed to orthograde.
Latin prōnus, leaning forward; see prone + -gradus, walking (from gradī, to move; see retrograde).(American Heritage® Dictionary of the English Language, Fourth Edition)