Directional terms come in opposing pairs (like East/West and North/South).
Anatomical planes describe cadaver cuts made in order to view exposed structures.
Muscle & Joint Actions
Muscle & joint actions are described by opposing terms. Muscles act by moving joints.
Veterinary vs Human Terms
Certain Direction & Plane terms have conflicting meanings in human and veterinary anatomy.
An Atlas of Animal Anatomy for Artists
By W. Ellenberger; Dover Publications, New York 1949