Supine: This refers to having the back or dorsal surface downward. A person who is in a supine position is lying face up as opposed to prone.
For a more complete listing of terms used in medicine for spatial orientation, please see the entry to "Anatomic Orientation Terms".
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References
Jameson, J. Larry, et al. Harrison's Principles of Internal Medicine, 20th Ed. New York: McGraw-Hill Education, 2018.