。
There's a little path running between the fields.
Literal
Field [gen-の] between [in-に] 1-[counter-本] little-path [subj-が] exists-[polite-ます].
1本 uses the counter 本 for long thin objects (including paths, lines, rivers, bottles, pens). The counter is obligatory in Japanese for counting — '1 path' is ungrammatical; one must specify 一本. 野原の間 ('between the fields') uses 間 ('interval, between'), taking the possessive の with the flanking items.