Glossary

 Track and Paw Illustration Of Length
Length of Dog Track

Proximal

Relating to, or located towards, the center of the main body.

In the case of an appendage, such as a limb, this is towards the point of attachment to the main body.

Proximal Direction Illustrated by Dog Paw

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Length (of a Track)
The distance from the proximal  edge of a track to the distal  point or edge (leading edge), measured parallel to the foot axis.
Cf. width (of a track)

Dog Footprint in Sand Illustrating Length

Dog Track in Sand (Illustrating Length of a Track)